[cssom] Use an interface instead of sequence for CSSRuleList and StyleSheetList, since there may be content that rely on item() working. Align with DOM's NodeList. https://www.w3.org/Bugs/Public/show_bug.cgi?id=22133

Author: Simon Pieters

cssom/Overview.src.html

@@ -1112,11 +1112,21 @@ <h4>The HTTP <code title>Default-Style</code> Header</h4>
   value of the header.</p>
 
 
-  <h4>The <code title>StyleSheetList</code> Sequence</h4>
+  <h4>The <code title>StyleSheetList</code> Interface</h4>
 
-<pre class=idl>typedef sequence&lt;<span>StyleSheet</span>> <span>StyleSheetList</span>;</pre>
-<p>The <dfn>StyleSheetList</dfn> sequence represents an ordered collection of <span title='style sheets'>style sheets</span>.</p>
+<p>The <code>StyleSheetList</code> interface represents an ordered collection of <span>style sheets</span>.</p>
 
+<pre class=idl>[ArrayClass]
+interface <dfn>StyleSheetList</dfn> {
+  getter <span>StyleSheet</span>? <span title=dom-StyleSheetList-item>item</span>(unsigned long index);
+  readonly attribute unsigned long <span title=dom-StyleSheetList-length>length</span>;
+};</pre>
+
+<p>The object's <span data-anolis-spec=webidl>supported property indices</span> are the numbers in the range zero to one less than the number of <span>style sheets</span> represented by the collection. If there are no such <span>style sheets</span>, then there are no <span data-anolis-spec=webidl>supported property indices</span>.
+
+<p>The <dfn title=dom-StyleSheetList-item><code>item(<var>index</var>)</code></dfn> method must return the <var>index</var>th <span>style sheet</span> in the collection. If there is no <var>index</var>th object in the collection, then the method must return <code>null</code>.
+
+<p>The <dfn title=dom-StyleSheetList-length><code>length</code></dfn> attribute must return the number of <span>style sheets</span> represented by the collection.
 
   <h4>Extensions to the <code title>Document</code> Interface</h4>
 
@@ -1177,7 +1187,7 @@ <h4>Extensions to the <code title>Document</code> Interface</h4>
   void <span title=dom-Document-enableStyleSheetsForSet>enableStyleSheetsForSet</span>(DOMString? name);<!-- new -->
 };</pre>
 
-<p>The <dfn title=dom-Document-styleSheets><code>styleSheets</code></dfn> attribute must return a <code>StyleSheetList</code> sequence representing
+<p>The <dfn title=dom-Document-styleSheets><code>styleSheets</code></dfn> attribute must return a <code>StyleSheetList</code> collection representing
 the <span>document style sheets</span>.</p>
 <p class='note'>Because of historical IDL limitations the <code title=dom-Document-styleSheets>styleSheets</code> attribute
 used to be on a separate interface, <code>DocumentStyle</code>.</p>
@@ -1673,12 +1683,21 @@ <h3>CSS Rules</h3>
   </dl>
 
 
-  <h4>The <code title>CSSRuleList</code> Sequence</h4>
+  <h4>The <code title>CSSRuleList</code> Interface</h4>
+
+<p>The <code>CSSRuleList</code> interface represents an ordered collection of CSS style rules.</p>
+
+<pre class=idl>[ArrayClass]
+interface <dfn>CSSRuleList</dfn> {
+  getter <span>CSSRule</span>? <span title=dom-CSSRuleList-item>item</span>(unsigned long index);
+  readonly attribute unsigned long <span title=dom-CSSRuleList-length>length</span>;
+};</pre>
 
-<pre class=idl>typedef sequence&lt;<span>CSSRule</span>> <span>CSSRuleList</span>;</pre>
+<p>The object's <span data-anolis-spec=webidl>supported property indices</span> are the numbers in the range zero to one less than the number of <code>CSSRule</code> objects represented by the collection. If there are no such <code>CSSRule</code> objects, then there are no <span data-anolis-spec=webidl>supported property indices</span>.
 
-<p>The <dfn><code>CSSRuleList</code></dfn> sequence represents an ordered collection of CSS style rules.</p>
+<p>The <dfn title=dom-StyleSheetList-item><code>item(<var>index</var>)</code></dfn> method must return the <var>index</var>th <code>CSSRule</code> object in the collection. If there is no <var>index</var>th object in the collection, then the method must return <code>null</code>.
 
+<p>The <dfn title=dom-StyleSheetList-length><code>length</code></dfn> attribute must return the number of <code>CSSRule</code> objects represented by the collection.
 
   <h4>The <code title>CSSRule</code> Interface</h4>