Allow "bulk editing" of the CssStyleDeclaration objects in an ElementList as well

tools/dom/templates/html/impl/impl_CSSStyleDeclaration.darttemplate

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of $LIBRARYNAME;
 
-$(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
+$(ANNOTATIONS)$(CLASS_MODIFIERS) class $CLASSNAME $EXTENDS with 
+    $(CLASSNAME)Mixin $IMPLEMENTS$NATIVESPEC {
   factory $CLASSNAME() => new CssStyleDeclaration.css('');
 
   factory $CLASSNAME.css(String css) {
     final style = new Element.tag('div').style;
     style.cssText = css;
     return style;
   }
+}
 
+/**
+ * A collection of [CssStyleDeclaration]s that are associated with an
+ * [ElementList].
+ *
+ * Grouping the style objects all together provides easy editing of specific
+ * properties of a collection of elements. Setting a specific property value
+ * will set that property in all [Element]s in the [ElementList]. Getting a
+ * specific property value will return the value of the property of the first
+ * element in the [ElementList].
+ */
+class $(CLASSNAME)Set $EXTENDS with $(CLASSNAME)Mixin {

[blois, 2013/07/30 00:45:18]

I don't think that this one should extend Interceptor, just Object.

Also probably just use the class name rather than $CLASSNAME macro, it's more
readable here and stuff cannot be renamed without code changes anyways.

+  final Iterable<Element> _elementIterable;
+  Iterable<$(CLASSNAME)> _elementCssStyleDeclarationSetIterable;
+
+  $(CLASSNAME)Set._(this._elementIterable) {
+    _elementCssStyleDeclarationSetIterable = new List.from(
+        _elementIterable).map((e) => e.style);
+  }
+
+  String getPropertyValue(String propertyName) =>
+      _elementCssStyleDeclarationSetIterable.first.getPropertyValue(
+          propertyName);
+
+  void setProperty(String propertyName, String value, [String priority]) {
+    _elementCssStyleDeclarationSetIterable.forEach((e) =>
+        e.setProperty(propertyName, value, priority));
+  }
+  // Important note: CssStyleDeclarationSet does NOT implement every method
+  // available in CssStyleDeclaration. Some of the methods don't make so much
+  // sense in terms of having a resonable value to return when you're
+  // considering a list of Elements. You will need to manually add any of the
+  // items in the MEMBERS set if you want that functionality.
+}
+
+abstract class $(CLASSNAME)Mixin {
 $!MEMBERS
-
   String getPropertyValue(String propertyName) {

[blois, 2013/07/30 00:45:18]

This should probably be on the single element one, no?

     var propValue = _getPropertyValue(propertyName);
     return propValue != null ? propValue : '';
   }
 
 $if DART2JS
   @DomName('CSSStyleDeclaration.setProperty')
   void setProperty(String propertyName, String value, [String priority]) {
     // try/catch for IE9 which throws on unsupported values.
     try {
       if (priority == null) {
         priority = '';
       }
       JS('void', '#.setProperty(#, #, #)', this, propertyName, value, priority);
       // Bug #2772, IE9 requires a poke to actually apply the value.
       if (JS('bool', '!!#.setAttribute', this)) {
         JS('void', '#.setAttribute(#, #)', this, propertyName, value);
       }
     } catch (e) {}
   }
 
   /**
    * Checks to see if CSS Transitions are supported.
    */
   static bool get supportsTransitions {

[blois, 2013/07/30 00:45:18]

Since its a static, should be on the CssStyleDeclaration rather than mixin.

     if (JS('bool', '"transition" in document.body.style')) {
       return true;
     }
     var propertyName = '${Device.propertyPrefix}Transition';
     return JS('bool', '# in document.body.style', propertyName);
   }
 $else
   /**
    * Checks to see if CSS Transitions are supported.
    */
@@ skipping 3165 matching lines @@
 
   /** Gets the value of "zoom" */
   String get zoom =>
     getPropertyValue('zoom');
 
   /** Sets the value of "zoom" */
   void set zoom(String value) {
     setProperty('zoom', value, '');
   }
 }