cc : Stop pushing layers from hidden subtrees at commit

cc/trees/tree_synchronizer.cc

Index: cc/trees/tree_synchronizer.cc
diff --git a/cc/trees/tree_synchronizer.cc b/cc/trees/tree_synchronizer.cc
index 87efee06cab3859b3382d1fbd7e7c8d6e07037b5..572333fef3e3c1644665b1f35cbfe774dfad95d2 100644
--- a/cc/trees/tree_synchronizer.cc
+++ b/cc/trees/tree_synchronizer.cc
@@ -93,26 +93,37 @@ static bool LayerHasValidPropertyTreeIndices(LayerImpl* layer) {
 }
 #endif
 
+static bool IsHidden(Layer* layer) {
+  return layer->is_hidden();
+}
+
+static bool IsHidden(LayerImpl* layer) {
+  return false;
+}
+
 template <typename LayerTreeType>
 void PushLayerList(OwnedLayerImplMap* old_layers,
                    LayerTreeType* host,
                    LayerTreeImpl* tree_impl) {
   tree_impl->ClearLayerList();
   for (auto* layer : *host) {
-    std::unique_ptr<LayerImpl> layer_impl(
-        ReuseOrCreateLayerImpl(old_layers, layer, tree_impl));
+    // TODO(crbug.com/726535) : Try not pushing all skipped layers and not just
+    // the hidden layers here.
+    if (!IsHidden(layer)) {
+      std::unique_ptr<LayerImpl> layer_impl(
+          ReuseOrCreateLayerImpl(old_layers, layer, tree_impl));
 
 #if DCHECK_IS_ON()
-    // Every layer should have valid property tree indices
-    AssertValidPropertyTreeIndices(layer);
-    // Every layer_impl should either have valid property tree indices already
-    // or the corresponding layer should push them onto layer_impl.
-    DCHECK(LayerHasValidPropertyTreeIndices(layer_impl.get()) ||
-           host->LayerNeedsPushPropertiesForTesting(layer));
+      // Every layer should have valid property tree indices
+      AssertValidPropertyTreeIndices(layer);
+      // Every layer_impl should either have valid property tree indices already
+      // or the corresponding layer should push them onto layer_impl.
+      DCHECK(LayerHasValidPropertyTreeIndices(layer_impl.get()) ||
+             host->LayerNeedsPushPropertiesForTesting(layer));
 #endif
-
-    tree_impl->AddToLayerList(layer_impl.get());
-    tree_impl->AddLayer(std::move(layer_impl));
+      tree_impl->AddToLayerList(layer_impl.get());
+      tree_impl->AddLayer(std::move(layer_impl));
+    }
   }
   tree_impl->OnCanDrawStateChangedForTree();
 }
@@ -122,9 +133,11 @@ static void PushLayerPropertiesInternal(
     std::unordered_set<LayerType*> layers_that_should_push_properties,
     LayerTreeImpl* impl_tree) {
   for (auto layer : layers_that_should_push_properties) {
-    LayerImpl* layer_impl = impl_tree->LayerById(layer->id());
-    DCHECK(layer_impl);
-    layer->PushPropertiesTo(layer_impl);
+    if (!IsHidden(layer)) {
+      LayerImpl* layer_impl = impl_tree->LayerById(layer->id());
+      DCHECK(layer_impl);
+      layer->PushPropertiesTo(layer_impl);
+    }
   }
 }