cc: Make animated opacity trigger render surface creation

This makes layers with animated opacity get treated as though they
have non-1 opacity when determining whether they need a render surface,
since an animation can cause opacity to change from 1 to non-1 without
a commit happening in between.

CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_blink_rel

Review-Url: https://codereview.chromium.org/2169143002
Cr-Commit-Position: refs/heads/master@{#407142}

cc/trees/layer_tree_host_common_unittest.cc

@@ -8503,6 +8503,34 @@ TEST_F(LayerTreeHostCommonTest,
             descendant_of_animation->visible_layer_rect_for_testing());
 }
 
+// Verify that having animated opacity but current opacity 1 still creates
+// a render surface.
+TEST_F(LayerTreeHostCommonTest, AnimatedOpacityCreatesRenderSurface) {
+  LayerImpl* root = root_layer_for_testing();
+  LayerImpl* child = AddChild<LayerImpl>(root);
+  LayerImpl* grandchild = AddChild<LayerImpl>(child);
+  child->SetDrawsContent(true);
+  grandchild->SetDrawsContent(true);
+
+  gfx::Transform identity_transform;
+  SetLayerPropertiesForTesting(root, identity_transform, gfx::Point3F(),
+                               gfx::PointF(), gfx::Size(50, 50), true, false);
+  SetLayerPropertiesForTesting(child, identity_transform, gfx::Point3F(),
+                               gfx::PointF(), gfx::Size(50, 50), true, false);
+  SetLayerPropertiesForTesting(grandchild, identity_transform, gfx::Point3F(),
+                               gfx::PointF(), gfx::Size(50, 50), true, false);
+
+  SetElementIdsForTesting();
+  AddOpacityTransitionToElementWithPlayer(child->element_id(), timeline_impl(),
+                                          10.0, 1.f, 0.2f, false);
+  ExecuteCalculateDrawProperties(root);
+
+  EXPECT_EQ(1.f, child->Opacity());
+  EXPECT_TRUE(root->has_render_surface());
+  EXPECT_TRUE(child->has_render_surface());
+  EXPECT_FALSE(grandchild->has_render_surface());
+}
+
 // Verify that having an animated filter (but no current filter, as these
 // are mutually exclusive) correctly creates a render surface.
 TEST_F(LayerTreeHostCommonTest, AnimatedFilterCreatesRenderSurface) {

cc/trees/property_tree_builder.cc

@@ -882,7 +882,9 @@ bool ShouldCreateRenderSurface(LayerType* layer,
       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",