[cssom] Remove API for alternative stylesheets

Remove Document#selectedStyleSheetSet, lastStyleSheetSet,
preferredStyleSheetSet, styleSheetSets, enableStyleSheetsForSet().

Fixes https://www.w3.org/Bugs/Public/show_bug.cgi?id=29471.

Author: zcorpan

cssom/Overview.bs

@@ -1156,11 +1156,6 @@ represented by the collection.
 <pre class=idl>
 partial interface Document {
   [SameObject] readonly attribute StyleSheetList styleSheets;
-  attribute DOMString? selectedStyleSheetSet;
-  readonly attribute DOMString? lastStyleSheetSet;
-  readonly attribute DOMString? preferredStyleSheetSet;
-  readonly attribute FrozenArray&lt;DOMString> styleSheetSets;
-  void enableStyleSheetsForSet(DOMString? name);
 };
 </pre>
 
@@ -1169,180 +1164,6 @@ the <a>document CSS style sheets</a>.
 Note: Because of historical IDL limitations the {{Document/styleSheets}} attribute
 used to be on a separate interface, <code>DocumentStyle</code>.
 
-The <dfn attribute for=Document>selectedStyleSheetSet</dfn> attribute, on getting, must run these steps:
-<ol>
- <li>If there is a single <a>enabled CSS style sheet set</a> and no
- other <a>document CSS style sheets</a> with a
- <a>title</a> that is not the empty string have the
- <a>disabled flag</a> unset, return the
- <a>CSS style sheet set name</a> of the
- <a>enabled CSS style sheet set</a> and terminate these steps.
-
- <li>Otherwise, if <a>CSS style sheets</a> from
- different <a lt="CSS style sheet set">CSS style sheet sets</a> have
- their <a>disabled flag</a> unset, return
- null and terminate these steps.
-
- <li>
-  Otherwise, return the empty string.
-
-  Note: At this point either all
-  <a>CSS style sheets</a> with a
-  <a>title</a> that is not the empty string have the
-  <a>disabled flag</a> set, or there are no such
-  <a>CSS style sheets</a>.
-
-</ol>
-
-On setting the
-{{Document/selectedStyleSheetSet}}
-attribute these steps must be run:
-
-<ol>
- <li>If the value is null terminate this set of steps.
- <li>Otherwise, <a>select a CSS style sheet set</a> with the name being the
- value passed.
-</ol>
-
-From the DOM's perspective, all views have the same
-{{Document/selectedStyleSheetSet}}.
-If a user agent supports multiple views with different selected
-alternative style sheets, then this attribute (and the
-{{StyleSheet}} interface's
-{{StyleSheet/disabled}} attribute)
-must return and set the value for the default
-view.
-
-The <dfn attribute for=Document>lastStyleSheetSet</dfn> attribute must return the <a>last CSS style sheet set name</a>.
-Note: This attribute is initially null.
-
-The <dfn attribute for=Document>preferredStyleSheetSet</dfn> attribute must return the <a>preferred CSS style sheet set
-name</a>.
-Note: Unlike {{Document/lastStyleSheetSet}},
-this attribute is initially the empty string.
-
-The <dfn attribute for=Document>styleSheetSets</dfn> attribute must return a frozen array of the
-<a lt="CSS style sheet set name">CSS style sheet set names</a> of the <a lt="CSS style sheet set">CSS style sheet sets</a>, in order of the
-<a>document CSS style sheets</a>. The array is live; if the <a>document CSS style sheets</a> change, the array must be updated as appropriate.
-
-The <dfn method for=Document>enableStyleSheetsForSet(<var>name</var>)</dfn> method must, when invoked, run these
-steps:
-<ol>
- <li>If <var>name</var> is null terminate these steps.
- <li><a>enable a CSS style sheet set</a> with name <var>name</var>.
-</ol>
-Note: <a>CSS style sheets</a> with a
-<a>title</a> that is the empty string are never affected by this method.
-This method does not change the values of the
-{{Document/lastStyleSheetSet}} or
-{{Document/preferredStyleSheetSet}} attributes.
-
-
-### Interaction with the User Interface ### {#interaction-with-the-user-interface}
-
-The user interface of Web browsers that support style sheets
-should list the style sheet titles given in the
-<code lt="dom-Document-styleSheetSets">styleSheetSets</code> list,
-showing the
-<code lt="dom-Document-selectedStyleSheetSet">selectedStyleSheetSet</code>
-as the selected style sheet set, leaving none selected if it is
-null or the empty string, and selecting an extra option
-"Basic Page Style" (or similar) if it is the empty string and the
-<code lt="dom-Document-preferredStyleSheetSet">preferredStyleSheetSet</code>
-is the empty string as well.
-
-Selecting a style sheet from this list should
-use the <a>select a CSS style sheet set</a> set of steps. This
-(by definition) affects the
-<code lt="dom-Document-lastStyleSheetSet">lastStyleSheetSet</code>
-attribute.
-
-#### Persisting the selected CSS style sheet set #### {#persisting-the-selected-css-style-sheet-set}
-
-If a user agent persist the <a lt="select a CSS style sheet set">selected</a> <a>CSS style sheet set</a>, it should use
-the value of the
-<code lt="dom-Document-selectedStyleSheetSet">selectedStyleSheetSet</code>
-attribute, or if that is null, the
-<code lt="dom-Document-lastStyleSheetSet">lastStyleSheetSet</code>
-attribute, when leaving the page (or at some other time) to determine the
-set name to store. If that is null then the <a>CSS style sheet set</a> should not be
-persisted.
-
-When re-setting the <a>CSS style sheet set</a> to the persisted value (which can
-happen at any time, typically at the first time the <a>CSS style sheets</a> are
-needed for styling the document, after the <code>&lt;head&gt;</code> of
-the document has been parsed, after any scripts that are not dependent on
-computed style have executed), the <a>CSS style sheet set</a>
-should be set by using the
-<a>select a CSS style sheet set</a> set of steps as if the user had
-selected the <a>CSS style sheet set</a> manually.
-
-Note: This specification does not give any suggestions on
-how user agents are to decide to persist the <a>CSS style sheet set</a> or whether or
-how to persist the <a lt="select a CSS style sheet set">selected</a> <a>CSS style sheet set</a> across pages.
-
-<!-- XXX this UI section suggests we may want to introduce a few more
-     idioms -->
-
-
-### Examples ### {#css-style-sheet-collections-examples}
-
-<div class="example">
- Thus, in the following HTML snippet:
-
- <pre>
- &lt;link rel="alternate stylesheet" lt="foo" href="a"&gt;
- &lt;link rel="alternate stylesheet" lt="bar" href="b"&gt;
- &lt;script&gt;
-   document.selectedStyleSheetSet = 'foo';
-   document.styleSheets[1].disabled = false;
- &lt;/script&gt;
- &lt;link rel="alternate stylesheet" lt="foo" href="c"&gt;
- &lt;link rel="alternate stylesheet" lt="bar" href="d"&gt;
- </pre>
-
- ...the style sheets that end up enabled are style sheets "a", "b",
- and "c", the
- <code lt="dom-Document-selectedStyleSheetSet">selectedStyleSheetSet</code>
- attribute would return null,
- <code lt="dom-Document-lastStyleSheetSet">lastStyleSheetSet</code>
- would return "foo", and
- <code lt="dom-Document-preferredStyleSheetSet">preferredStyleSheetSet</code>
- would return the empty string.
-
- Similarly, in the following HTML snippet:
-
- <pre>
- &lt;link rel="alternate stylesheet" lt="foo" href="a"&gt;
- &lt;link rel="alternate stylesheet" lt="bar" href="b"&gt;
- &lt;script&gt;
-   var before = document.preferredStyleSheetSet;
-   document.styleSheets[1].disabled = false;
- &lt;/script&gt;
- &lt;link rel="stylesheet" lt="foo" href="c"&gt;
- &lt;link rel="alternate stylesheet" lt="bar" href="d"&gt;
- &lt;script&gt;
-   var after = document.preferredStyleSheetSet;
- &lt;/script&gt;
- </pre>
-
- ...the "before" variable will be equal to the empty string, the
- "after" variable will be equal to "foo", and style sheets "a" and "c"
- will be enabled. This is the case even though the first script block
- sets style sheet "b" to be enabled, because upon parsing the
- following <code>&lt;link&gt;</code> element, the
- <code lt="dom-Document-preferredStyleSheetSet">preferredStyleSheetSet</code>
- is set and the
- <code lt="dom-Document-enableStyleSheetsForSet()">enableStyleSheetsForSet()</code>
- method is called (since
- <code lt="dom-Document-selectedStyleSheetSet">selectedStyleSheetSet</code>
- was never set
- explicitly, leaving
- <code lt="dom-Document-lastStyleSheetSet">lastStyleSheetSet</code> at
- null throughout), which changes which style sheets are enabled and which
- are not.
-</div>
-
 
 Style Sheet Association {#style-sheet-association}
 --------------------------------------------------
@@ -3081,6 +2902,11 @@ CSSCharsetRule is re-dropped.
 GetStyleUtils is dropped.
 Element#pseudo() is dropped.
 PseudoElement is dropped.
+Document#selectedStyleSheetSet is dropped.
+Document#lastStyleSheetSet is dropped.
+Document#preferredStyleSheetSet is dropped.
+Document#styleSheetSets is dropped.
+Document#enableStyleSheetsForSet() is dropped.
 
 -->