Add fixed raster scale use counter histograms.

cc/test/fake_layer_tree_host_client.h

Index: cc/test/fake_layer_tree_host_client.h
diff --git a/cc/test/fake_layer_tree_host_client.h b/cc/test/fake_layer_tree_host_client.h
index 1684e3eaa1114119b3e7476c43cf607109babb69..fc7fa752de7b6b43e9ddd10c1aca845e5229ac14 100644
--- a/cc/test/fake_layer_tree_host_client.h
+++ b/cc/test/fake_layer_tree_host_client.h
@@ -54,6 +54,10 @@ class FakeLayerTreeHostClient : public LayerTreeHostClient,
   void DidPostSwapBuffers() override {}
   void DidAbortSwapBuffers() override {}
 
+  void ReportFixedRasterScaleUseCounters(

[danakj, 2016/05/05 00:09:49]

this should be part of the LayerTreeHostClient impl block

[vmpstr, 2016/05/05 01:33:50]

Done.

+      bool has_blurry_content,
+      bool has_potential_performance_regression) override {}
+
  private:
   bool use_software_rendering_;
   bool use_delegating_renderer_;