Add UseCounter for Element.createShadowRoot()

BUG=383749
TEST=none
R=yutak@chromium.org

Review URL: https://codereview.chromium.org/334833003

git-svn-id: svn://svn.chromium.org/blink/trunk@176093 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/dom/Element.idl

@@ -108,7 +108,7 @@
     [RaisesException, ImplementedAs=matches, MeasureAs=ElementPrefixedMatchesSelector] boolean webkitMatchesSelector(DOMString selectors);
 
     // Shadow DOM API
-    [RaisesException] ShadowRoot createShadowRoot();
+    [RaisesException, MeasureAs=ElementCreateShadowRoot] ShadowRoot createShadowRoot();
     [PerWorldBindings] readonly attribute ShadowRoot shadowRoot;
     [PerWorldBindings] NodeList getDestinationInsertionPoints();
 

third_party/WebKit/Source/core/frame/UseCounter.h

@@ -453,6 +453,7 @@ public:
         WebkitEditableContentChangedOnContentEditable = 453,
         WebkitEditableContentChangedOnNotNode = 454,
         HTMLImports = 455,
+        ElementCreateShadowRoot = 456,
         // Add new features immediately above this line. Don't change assigned
         // numbers of any item, and don't reuse removed slots.
         // Also, run update_use_counter_feature_enum.py in chromium/src/tools/metrics/histograms/