cc/blimp: Eliminate Layer updates for common cases.

cc/blimp/layer_tree_host_remote_unittest.cc

Index: cc/blimp/layer_tree_host_remote_unittest.cc
diff --git a/cc/blimp/layer_tree_host_remote_unittest.cc b/cc/blimp/layer_tree_host_remote_unittest.cc
index 8cd6d6d439db2426ab6048250d5deecd98a415aa..08f2bf6d6b68a42f553c3205cc5f66657b5b4f28 100644
--- a/cc/blimp/layer_tree_host_remote_unittest.cc
+++ b/cc/blimp/layer_tree_host_remote_unittest.cc
@@ -413,5 +413,42 @@ TEST_F(LayerTreeHostRemoteTest, ScrollAndScaleSync) {
   EXPECT_FALSE(updates_applied);
 }
 
+TEST_F(LayerTreeHostRemoteTest, IdentifiedLayersToSkipUpdates) {
+  EXPECT_BEGIN_MAIN_FRAME_AND_COMMIT(mock_layer_tree_host_client_, 1);
+
+  scoped_refptr<MockLayer> non_drawable_layer = new MockLayer(true);
+  non_drawable_layer->SetIsDrawable(false);
+  non_drawable_layer->SetBounds(gfx::Size(5, 5));
+
+  scoped_refptr<MockLayer> empty_bound_layer = new MockLayer(true);

[ajuma, 2016/11/01 21:37:07]

nit: empty_bounds_layer

+  empty_bound_layer->SetIsDrawable(true);
+  empty_bound_layer->SetBounds(gfx::Size());
+
+  scoped_refptr<MockLayer> transparent_layer = new MockLayer(true);
+  transparent_layer->SetIsDrawable(true);
+  transparent_layer->SetBounds(gfx::Size(5, 5));
+  transparent_layer->SetOpacity(0.f);
+
+  scoped_refptr<MockLayer> updated_layer = new MockLayer(true);
+  updated_layer->SetIsDrawable(true);
+  updated_layer->SetBounds(gfx::Size(5, 5));
+
+  root_layer_->AddChild(non_drawable_layer);
+  root_layer_->AddChild(empty_bound_layer);
+  empty_bound_layer->SetMaskLayer(transparent_layer.get());
+  empty_bound_layer->AddChild(updated_layer);
+  DCHECK(updated_layer->GetLayerTreeHostForTesting());
+
+  // Commit and serialize.
+  layer_tree_host_->SetNeedsCommit();
+  base::RunLoop().RunUntilIdle();
+
+  // Only the updated_layer should have been updated.
+  EXPECT_FALSE(non_drawable_layer->did_update());
+  EXPECT_FALSE(empty_bound_layer->did_update());
+  EXPECT_FALSE(transparent_layer->did_update());
+  EXPECT_TRUE(updated_layer->did_update());
+}
+
 }  // namespace
 }  // namespace cc