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

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

Index: tools/dom/templates/html/impl/impl_CSSStyleDeclaration.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_CSSStyleDeclaration.darttemplate b/tools/dom/templates/html/impl/impl_CSSStyleDeclaration.darttemplate
index 984f10d488dc72090da58ce0bfdccd9eed6f7568..192e95992f7ca8114a24526fb7a04728c1a0c7d0 100644
--- a/tools/dom/templates/html/impl/impl_CSSStyleDeclaration.darttemplate
+++ b/tools/dom/templates/html/impl/impl_CSSStyleDeclaration.darttemplate
@@ -4,7 +4,8 @@
 
 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) {
@@ -12,9 +13,44 @@ $(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
     style.cssText = css;
     return style;
   }
+}
 
-$!MEMBERS
+/**
+ * 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 : '';