Make the Sk GL context class an abstract base class

tools/timer/Timer.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef Timer_DEFINED
 #define Timer_DEFINED
 
 #include "SkTypes.h"
 
 #if defined(SK_BUILD_FOR_WIN32)
     #include "SysTimer_windows.h"
 #elif defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_IOS)
     #include "SysTimer_mach.h"
 #elif defined(SK_BUILD_FOR_UNIX) || defined(SK_BUILD_FOR_ANDROID)
     #include "SysTimer_posix.h"
 #endif
 
 #if SK_SUPPORT_GPU
     #include "GpuTimer.h"
 #endif
 
-class SkGLContextHelper;
+class SkGLContext;
 
 /**
  * SysTimers and GpuTimers are implemented orthogonally.
  * This class combines 2 SysTimers and a GpuTimer into one single,
  * platform specific Timer with a simple interface. The truncated
  * timer doesn't include the time required for the GPU to finish
  * its rendering. It should always be <= the un-truncated system
  * times and (for GPU configurations) can be used to roughly (very
  * roughly) gauge the GPU load/backlog.
  */
 class Timer {
 public:
-    explicit Timer(SkGLContextHelper* gl = NULL);
+    explicit Timer(SkGLContext* gl = NULL);
 
     void start();
     void truncatedEnd();
     void end();
 
     // All times in milliseconds.
     double fCpu;
     double fWall;
     double fTruncatedCpu;
     double fTruncatedWall;
@@ skipping 16 matching lines @@
     void start();
     void end();
 
     double fWall;  // Milliseconds.
 
 private:
     SysTimer fSysTimer;
 };
 
 #endif