bindings: Removes two FIXMEs because setReturnValueFast is useful.

I've benchmarked and found that DOMDataStore::setReturnValueFast
is quite effective for document.implementation and
getElementsByTagName.  We should keep this method.

BUG=235436

Review URL: https://codereview.chromium.org/702523003

git-svn-id: svn://svn.chromium.org/blink/trunk@185175 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/bindings/core/v8/DOMDataStore.h

@@ -65,7 +65,6 @@ public:
     {
         // The second fastest way to check if we're in the main world is to check if
         // the wrappable's wrapper is the same as the holder.
-        // FIXME: Investigate if it's worth having this check for performance.
         if (holderContainsWrapper(holder, wrappable))
             return object->setReturnValue(returnValue);
         return current(returnValue.GetIsolate()).setReturnValueFrom(returnValue, object);
@@ -76,7 +75,6 @@ public:
         if (canUseScriptWrappable(node)
             // The second fastest way to check if we're in the main world is to
             // check if the wrappable's wrapper is the same as the holder.
-            // FIXME: Investigate if it's worth having this check for performance.
             || holderContainsWrapper(holder, wrappable))
             return ScriptWrappable::fromNode(node)->setReturnValue(returnValue);
         return current(returnValue.GetIsolate()).setReturnValueFrom(returnValue, ScriptWrappable::fromNode(node));