cc: Make animated opacity trigger render surface creation

cc/trees/property_tree_builder.cc

 // Copyright 2014 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/property_tree_builder.h"
 
 #include <stddef.h>
 
 #include <map>
 #include <set>
@@ skipping 856 matching lines @@
 
   // If the layer has some translucency and does not have a preserves-3d
   // transform style.  This condition only needs a render surface if two or more
   // layers in the subtree overlap. But checking layer overlaps is unnecessarily
   // costly so instead we conservatively create a surface whenever at least two
   // layers draw content for this subtree.
   bool at_least_two_layers_in_subtree_draw_content =
       num_descendants_that_draw_content > 0 &&
       (layer->DrawsContent() || num_descendants_that_draw_content > 1);
 
-  if (EffectiveOpacity(layer) != 1.f && ShouldFlattenTransform(layer) &&
+  bool may_have_transparency = EffectiveOpacity(layer) != 1.f ||
+                               HasPotentiallyRunningOpacityAnimation(layer);
+  if (may_have_transparency && ShouldFlattenTransform(layer) &&
       at_least_two_layers_in_subtree_draw_content) {
     TRACE_EVENT_INSTANT0(
         "cc", "PropertyTreeBuilder::ShouldCreateRenderSurface opacity",
         TRACE_EVENT_SCOPE_THREAD);
     DCHECK(!is_root);
     return true;
   }
   // If the layer has isolation.
   // TODO(rosca): to be optimized - create separate rendering surface only when
   // the blending descendants might have access to the content behind this layer
@@ skipping 551 matching lines @@
     color = SkColorSetA(color, 255);
   BuildPropertyTreesTopLevelInternal(
       root_layer, page_scale_layer, inner_viewport_scroll_layer,
       outer_viewport_scroll_layer, overscroll_elasticity_layer,
       elastic_overscroll, page_scale_factor, device_scale_factor, viewport,
       device_transform, property_trees, color);
   property_trees->ResetCachedData();
 }
 
 }  // namespace cc