Cleanup: Pass std::string as const reference from gpu/

gpu/tools/compositor_model_bench/shaders.h

Index: gpu/tools/compositor_model_bench/shaders.h
diff --git a/gpu/tools/compositor_model_bench/shaders.h b/gpu/tools/compositor_model_bench/shaders.h
index 459403542fd061b994277f6245a5df0fe3a3afb2..5aece20060a0248b9c734f645b250a4f931f71c4 100644
--- a/gpu/tools/compositor_model_bench/shaders.h
+++ b/gpu/tools/compositor_model_bench/shaders.h
@@ -26,7 +26,7 @@ enum ShaderID {
   SHADER_ID_MAX
 };
 
-ShaderID ShaderIDFromString(std::string name);
+ShaderID ShaderIDFromString(const std::string& name);
 std::string ShaderNameFromID(ShaderID id);
 
 void ConfigAndActivateShaderForNode(CCNode* n);