cc : Stop pushing layers from hidden subtrees at commit

cc/trees/layer_tree_host.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 1052 matching lines @@
   base::AutoReset<bool> painting(&in_paint_layer_contents_, true);
   bool did_paint_content = false;
   for (const auto& layer : update_layer_list) {
     did_paint_content |= layer->Update();
     *content_is_suitable_for_gpu &= layer->IsSuitableForGpuRasterization();
   }
   return did_paint_content;
 }
 
 void LayerTreeHost::AddLayerShouldPushProperties(Layer* layer) {
+  if (layer->is_hidden())

[enne (OOO), 2017/05/01 20:15:09]

This is a little awkward, here.  I think what you want to say is that if a layer
is hidden, it shouldn't push properties.  This says if a layer becomes hidden,
then ignore additional push properties requests.  I think those are not quite
the same?

And then the tree sychronizer redundantly fixes this up, so maybe this call
isn't needed here?

[jaydasika, 2017/05/01 23:41:39]

Yes, what we want to say is if a layer is hidden, it shouldn't push properties.

The reason I added this here is for this sequence : hide layer-> commit ->
change a property on hidden layer -> commit. 
Even during second commit, we don't want to push properties of the layer. But if
the layer tree topology hasn't changed, we won't do full tree sync and never hit
the code in tree synchronizer that deletes hidden layers from push properties
layer list.

I agree this is unnecessarily complex, maybe we should just check while pushing
properties if the layer is hidden and skip it there. 
    

[enne (OOO), 2017/05/02 01:46:01]

That sounds good!

[jaydasika, 2017/05/19 19:08:59]

Done.

+    return;
   layers_that_should_push_properties_.insert(layer);
 }
 
 void LayerTreeHost::RemoveLayerShouldPushProperties(Layer* layer) {
   layers_that_should_push_properties_.erase(layer);
 }
 
 std::unordered_set<Layer*>& LayerTreeHost::LayersThatShouldPushProperties() {
   return layers_that_should_push_properties_;
 }
@@ skipping 356 matching lines @@
 void LayerTreeHost::SetNeedsDisplayOnAllLayers() {
   for (auto* layer : *this)
     layer->SetNeedsDisplay();
 }
 
 void LayerTreeHost::SetHasCopyRequest(bool has_copy_request) {
   has_copy_request_ = has_copy_request;
 }
 
 }  // namespace cc