Adding polyfill support for custom elements.

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

Index: tools/dom/templates/html/impl/impl_Element.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_Element.darttemplate b/tools/dom/templates/html/impl/impl_Element.darttemplate
index cbea8c1aed4623ebbe6782df2bbf15f8827e0620..054c5e0eab520cda0e797214f581fa2bbd5581e5 100644
--- a/tools/dom/templates/html/impl/impl_Element.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Element.darttemplate
@@ -244,7 +244,7 @@ abstract class ElementList<T extends Element> extends ListBase<T> {
    */
   @Experimental()
   CssRect get marginEdge;
-$!STREAM_GETTER_SIGNATURES 
+$!STREAM_GETTER_SIGNATURES
 }
 
 // TODO(jacobr): this is an inefficient implementation but it is hard to see
@@ -1170,6 +1170,20 @@ $endif
     Point p = Element._offsetToHelper(parentOffset, parent);
     return new Point(p.x + current.offsetLeft, p.y + current.offsetTop);
   }
+
+$if DART2JS
+  @JSName('innerHTML')
+  @DomName('HTMLElement.innerHTML')
+  String get innerHtml;
+
+  void set innerHtml(String value) {
+    JS('', '#.innerHTML = #', this, value);
+    // Polyfill relies on mutation observers for upgrading, but we want it

[Jennifer Messerly, 2013/08/20 19:09:59]

Interesting that the polyfill works this way... do we have an issue or bug
number on the Polymer side we can reference?

does upgrade happen synchronously in other places, such as `new Element.tag` and
`clone`?

[blois, 2013/08/20 19:36:56]

It's synchronous in clone and document.createElement but for some reason (not
sure why), innerHTML does not upgrade- it waits for the sub-tree to be added to
the document then gets upgraded by mutation observers. It could be a polyfill
limitation.

If innerHtml is rare then we could require users explicitly upgrade if they need
synchronous behavior.

+    // immediate.
+    Platform.upgradeCustomElements(this);
+  }
+$endif
+
 $!MEMBERS
 }