Moving GraphicsContext and dependencies from core to platform.

Source/platform/graphics/Extensions3D.h

Index: Source/platform/graphics/Extensions3D.h
diff --git a/Source/core/platform/graphics/Extensions3D.h b/Source/platform/graphics/Extensions3D.h
similarity index 99%
rename from Source/core/platform/graphics/Extensions3D.h
rename to Source/platform/graphics/Extensions3D.h
index f321258fcfb4d5b3e3a068e6f17ac3979f05d18f..970b0fb8fd5df64d1d822312b9c70769d60893a8 100644
--- a/Source/core/platform/graphics/Extensions3D.h
+++ b/Source/platform/graphics/Extensions3D.h
@@ -26,6 +26,7 @@
 #ifndef Extensions3D_h
 #define Extensions3D_h
 
+#include "platform/PlatformExport.h"
 #include "platform/graphics/GraphicsTypes3D.h"
 
 #include "wtf/text/WTFString.h"
@@ -40,7 +41,7 @@ class ImageBuffer;
 // Calling any extension function not supported by the current context
 // must be a no-op; in particular, it may not have side effects. In
 // this situation, if the function has a return value, 0 is returned.
-class Extensions3D {
+class PLATFORM_EXPORT Extensions3D {
 public:
     ~Extensions3D();