Remove unused enum declaration ContextWebkit3d from HTMLCanvasElement::getContext()

Source/core/html/HTMLCanvasElement.cpp

Index: Source/core/html/HTMLCanvasElement.cpp
diff --git a/Source/core/html/HTMLCanvasElement.cpp b/Source/core/html/HTMLCanvasElement.cpp
index e84eacf3bb509305325d62e996b246c48cc15f87..5a5af507606c2d06a78e8d6ce826761c6f100645 100644
--- a/Source/core/html/HTMLCanvasElement.cpp
+++ b/Source/core/html/HTMLCanvasElement.cpp
@@ -153,8 +153,8 @@ CanvasRenderingContext* HTMLCanvasElement::getContext(const String& type, Canvas
     // context with any other type string will destroy any existing context.
     enum ContextType {
         Context2d,
-        ContextWebkit3d,
-        ContextExperimentalWebgl,
+        // Retain the enum values 'as is' as these are used by the histograms.
+        ContextExperimentalWebgl = 2,

[rune, 2014/08/22 12:15:50]

I think it would be safer to explicitly assign a value to each enum. See how
it's done for the Feature enum in the UseCounter class.

[rune, 2014/08/22 12:15:50]

I think it would be safer to explicitly assign a value to each enum. See how
it's done for the Feature enum in the UseCounter class.

         ContextWebgl,
         // Only add new items to the end and keep the order of existing items.

[rune, 2014/08/22 12:15:50]

The comment in UseCounter for Feature looks clearer:

// Do not change assigned numbers of existing items: add new features
// to the end of the list.

Please consider using that comment and move it to the top of the enum.

         ContextTypeCount,