Revert of Make the Sk GL context class an abstract base class

tools/timer/Timer.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "Timer.h"
 
-Timer::Timer(SkGLContext* gl)
+Timer::Timer(SkGLContextHelper* gl)
         : fCpu(-1.0)
         , fWall(-1.0)
         , fTruncatedCpu(-1.0)
         , fTruncatedWall(-1.0)
         , fGpu(-1.0)
 #if SK_SUPPORT_GPU
         , fGpuTimer(gl)
 #endif
         {}
 
@@ skipping 24 matching lines @@
 
 WallTimer::WallTimer() : fWall(-1.0) {}
 
 void WallTimer::start() {
     fSysTimer.startWall();
 }
 
 void WallTimer::end() {
     fWall = fSysTimer.endWall();
 }