Make GrResourceCache perf less sensitive to key length change

include/gpu/GrResourceKey.h

Index: include/gpu/GrResourceKey.h
diff --git a/include/gpu/GrResourceKey.h b/include/gpu/GrResourceKey.h
index 50a71459290574dd107262274aa96dbdcd1db392..a353dc21143766f0a1cb7a2a598e9c55dc2c375b 100644
--- a/include/gpu/GrResourceKey.h
+++ b/include/gpu/GrResourceKey.h
@@ -46,7 +46,10 @@ protected:
     }
 
     bool operator==(const GrResourceKey& that) const {
-        return 0 == memcmp(fKey.get(), that.fKey.get(), this->size());
+        return this->hash() == that.hash() &&
+                0 == memcmp(&fKey[kHash_MetaDataIdx + 1],
+                            &that.fKey[kHash_MetaDataIdx + 1],
+                            this->internalSize() - sizeof(uint32_t));
     }
 
     GrResourceKey& operator=(const GrResourceKey& that) {