move mutex construction out of the benchmarks.

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 "Benchmark.h"
 #include "SkMutex.h"
 #include "SkSharedMutex.h"
 #include "SkSpinlock.h"
 #include "SkString.h"
 
 template <typename Mutex>
 class MutexBench : public Benchmark {
 public:
     MutexBench(SkString benchPrefix) : fBenchName(benchPrefix += "UncontendedBenchmark") { }
     bool isSuitableFor(Backend backend) override {
         return backend == kNonRendering_Backend;
     }
 
 protected:
     const char* onGetName() override {
         return fBenchName.c_str();
     }
 
     void onDraw(const int loops, SkCanvas*) override {
-        Mutex mu;
         for (int i = 0; i < loops; i++) {
-            mu.acquire();
-            mu.release();
+            fMu.acquire();
+            fMu.release();
         }
     }
 
 private:
     typedef Benchmark INHERITED;
     SkString fBenchName;
+    Mutex fMu;
 };
 
 class SharedBench : public Benchmark {
 public:
     bool isSuitableFor(Backend backend) override {
         return backend == kNonRendering_Backend;
     }
 
 protected:
     const char* onGetName() override {
         return "SkSharedMutexSharedUncontendedBenchmark";
     }
 
     void onDraw(const int loops, SkCanvas*) override {
-        SkSharedMutex mu;
         for (int i = 0; i < loops; i++) {
-            mu.acquireShared();
-            mu.releaseShared();
+            fMu.acquireShared();
+            fMu.releaseShared();
         }
     }
 
 private:
     typedef Benchmark INHERITED;
+    SkSharedMutex fMu;
 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
 DEF_BENCH( return new MutexBench<SkSharedMutex>(SkString("SkSharedMutex")); )
 DEF_BENCH( return new MutexBench<SkMutex>(SkString("SkMutex")); )
 DEF_BENCH( return new MutexBench<SkSpinlock>(SkString("SkSpinlock")); )
 DEF_BENCH( return new SharedBench; )