Move GraphicsContextTest to platform/ and fix the test environment.

Source/platform/TestingPlatformSupport.h

 /*
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 49 matching lines @@
         bool hasDiscardableMemorySupport;
     };
 
     explicit TestingPlatformSupport(const Config&);
 
     virtual ~TestingPlatformSupport();
 
     // blink::Platform:
     virtual blink::WebDiscardableMemory* allocateAndLockDiscardableMemory(size_t bytes) OVERRIDE;
     virtual void cryptographicallyRandomValues(unsigned char* buffer, size_t length) OVERRIDE;
+    virtual const unsigned char* getTraceCategoryEnabledFlag(const char* categoryName) OVERRIDE;
 
 private:
     const Config m_config;
     blink::Platform* const m_oldPlatform;
 };
 
 } // namespace WebCore
 
 #endif // TestingPlatformSupport_h