Implement a benchmark for GrResourceCache

bench/WriterBench.cpp

Index: bench/WriterBench.cpp
diff --git a/bench/WriterBench.cpp b/bench/WriterBench.cpp
index 0956b22b10913859799502732790ef9d5971f60d..f9a0ac89b48c92cd525d40cdaaee7cc48def2d25 100644
--- a/bench/WriterBench.cpp
+++ b/bench/WriterBench.cpp
@@ -12,7 +12,9 @@
 
 class WriterBench : public SkBenchmark {
 public:
-    WriterBench() { fIsRendering = false; }
+    virtual bool isSuitableFor(Backend backend) SK_OVERRIDE {
+        return backend == kNonRendering_Backend;
+    }
 
 protected:
     virtual const char* onGetName() SK_OVERRIDE {