[cssom] Make setProperty's value argument have [TreatNullAs=EmptyString]. https://www.w3.org/Bugs/Public/show_bug.cgi?id=22266

Author: Simon Pieters

cssom/Overview.html

@@ -2157,11 +2157,11 @@ <h4 id="the-cssstyledeclaration-interface"><span class="secno">6.5.1 </span>The
   getter DOMString <a href="#dom-cssstyledeclaration-item" title="dom-CSSStyleDeclaration-item">item</a>(unsigned long index);
   DOMString <a href="#dom-cssstyledeclaration-getpropertyvalue" title="dom-CSSStyleDeclaration-getPropertyValue">getPropertyValue</a>(DOMString property);
   DOMString <a href="#dom-cssstyledeclaration-getpropertypriority" title="dom-CSSStyleDeclaration-getPropertyPriority">getPropertyPriority</a>(DOMString property);
-  void <a href="#dom-cssstyledeclaration-setproperty" title="dom-CSSStyleDeclaration-setProperty">setProperty</a>(DOMString property, DOMString value, <!--
+  void <a href="#dom-cssstyledeclaration-setproperty" title="dom-CSSStyleDeclaration-setProperty">setProperty</a>(DOMString property, [TreatNullAs=EmptyString] DOMString value, <!--
   -->[TreatNullAs=EmptyString] optional DOMString priority = "");
   DOMString <a href="#dom-cssstyledeclaration-removeproperty" title="dom-CSSStyleDeclaration-removeProperty">removeProperty</a>(DOMString property);
   readonly attribute <a href="#cssrule">CSSRule</a>? <a href="#dom-cssstyledeclaration-length" title="dom-CSSStyleDeclaration-length">parentRule</a>;
-  [TreatNullAs=EmptyString] attribute DOMString <a href="#dom-cssstyledeclaration-cssfloat" title="dom-CSSStyleDeclaration-cssFloat">cssFloat</a>;
+           attribute DOMString <a href="#dom-cssstyledeclaration-cssfloat" title="dom-CSSStyleDeclaration-cssFloat">cssFloat</a>;<!-- setProperty's value arg has [TreatNullAs=EmptyString] -->
 };</pre>
 
 <p>The object's <a class="external" href="http://dev.w3.org/2006/webapi/WebIDL/#dfn-supported-property-indices">supported property indices</a> are the numbers in the range zero to one less than the number of declarations in
@@ -2270,7 +2270,7 @@ <h4 id="the-cssstyledeclaration-interface"><span class="secno">6.5.1 </span>The
 <var>property</var>.</p>
 
 <pre class="idl">partial interface <a href="#cssstyledeclaration">CSSStyleDeclaration</a> {
-  [TreatNullAs=EmptyString] attribute DOMString _<var title="dom-CSSStyleDeclaration-attribute"><a href="#dom-cssstyledeclaration-attribute">attribute</a></var>;
+           attribute DOMString _<var title="dom-CSSStyleDeclaration-attribute"><a href="#dom-cssstyledeclaration-attribute">attribute</a></var>;
 };</pre>
 
 <p>The <dfn id="dom-cssstyledeclaration-attribute" title="dom-CSSStyleDeclaration-attribute"><code><var title="">attribute</var></code></dfn> attribute, on getting, must return the result of invoking

cssom/Overview.src.html

@@ -2088,11 +2088,11 @@ <h4>The <code title>CSSStyleDeclaration</code> Interface</h4>
   getter DOMString <span title=dom-CSSStyleDeclaration-item>item</span>(unsigned long index);
   DOMString <span title=dom-CSSStyleDeclaration-getPropertyValue>getPropertyValue</span>(DOMString property);
   DOMString <span title=dom-CSSStyleDeclaration-getPropertyPriority>getPropertyPriority</span>(DOMString property);
-  void <span title=dom-CSSStyleDeclaration-setProperty>setProperty</span>(DOMString property, DOMString value, <!--
+  void <span title=dom-CSSStyleDeclaration-setProperty>setProperty</span>(DOMString property, [TreatNullAs=EmptyString] DOMString value, <!--
   -->[TreatNullAs=EmptyString] optional DOMString priority = "");
   DOMString <span title=dom-CSSStyleDeclaration-removeProperty>removeProperty</span>(DOMString property);
   readonly attribute <span>CSSRule</span>? <span title=dom-CSSStyleDeclaration-length>parentRule</span>;
-  [TreatNullAs=EmptyString] attribute DOMString <span title=dom-CSSStyleDeclaration-cssFloat>cssFloat</span>;
+           attribute DOMString <span title=dom-CSSStyleDeclaration-cssFloat>cssFloat</span>;<!-- setProperty's value arg has [TreatNullAs=EmptyString] -->
 };</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 declarations in
@@ -2201,7 +2201,7 @@ <h4>The <code title>CSSStyleDeclaration</code> Interface</h4>
 <var>property</var>.</p>
 
 <pre class=idl>partial interface <span>CSSStyleDeclaration</span> {
-  [TreatNullAs=EmptyString] attribute DOMString _<var title=dom-CSSStyleDeclaration-attribute>attribute</var>;
+           attribute DOMString _<var title=dom-CSSStyleDeclaration-attribute>attribute</var>;
 };</pre>
 
 <p>The <dfn title=dom-CSSStyleDeclaration-attribute><code><var title>attribute</var></code></dfn> attribute, on getting, must return the result of invoking