Implement a benchmark for GrResourceCache

bench/MutexBench.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 "SkBenchmark.h"
 #include "SkThread.h"
 
 class MutexBench : public SkBenchmark {
 public:
-    MutexBench()  {
-        fIsRendering = false;
+    virtual bool isSuitableFor(Backend backend) SK_OVERRIDE {
+        return backend == kNonRendering_Backend;
     }
+
 protected:
     virtual const char* onGetName() {
         return "mutex";
     }
 
     virtual void onDraw(SkCanvas*) {
         SK_DECLARE_STATIC_MUTEX(mu);
         for (int i = 0; i < this->getLoops(); i++) {
             mu.acquire();
             mu.release();
         }
     }
 
 private:
     typedef SkBenchmark INHERITED;
 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
 DEF_BENCH( return new MutexBench(); )