Remove some stray blink::WebGraphicsContext3D references from ui/

This type isn't used anywhere and doesn't need to be forward declared.

TBR=sky

Review URL: https://codereview.chromium.org/142713005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247890 0039d316-1c4b-4281-b951-d872f2087c98

ui/aura/bench/bench_main.cc

@@ -42,7 +42,6 @@ using base::TimeTicks;
 using ui::Compositor;
 using ui::Layer;
 using ui::LayerDelegate;
-using blink::WebGraphicsContext3D;
 
 namespace {
 

ui/compositor/compositor.h

@@ -28,10 +28,6 @@ class MessageLoopProxy;
 class RunLoop;
 }
 
-namespace blink {
-class WebGraphicsContext3D;
-}
-
 namespace cc {
 class ContextProvider;
 class Layer;