cc : Track ids for which active opacity always wins on property trees

cc/trees/layer_tree_host_impl_unittest.cc

Index: cc/trees/layer_tree_host_impl_unittest.cc
diff --git a/cc/trees/layer_tree_host_impl_unittest.cc b/cc/trees/layer_tree_host_impl_unittest.cc
index 264af100de4932b8c495fbeb8d4f0f65a64cbe2f..46478087be464bb5c34dd8f69c71cfbcb367b66c 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -2887,9 +2887,15 @@ class LayerTreeHostImplTestScrollbarOpacity : public LayerTreeHostImplTest {
     EffectNode* pending_tree_node =
         host_impl_->pending_tree()->property_trees()->effect_tree.Node(
             scrollbar_layer->effect_tree_index());
+    LayerImpl* pending_scrollbar_layer =
+        host_impl_->pending_tree()->LayerById(400);
+    host_impl_->pending_tree()
+        ->property_trees()
+        ->always_use_active_tree_opacity_effect_ids.push_back(400);
     EXPECT_FLOAT_EQ(1.f, active_tree_node->data.opacity);
     EXPECT_FLOAT_EQ(1.f, scrollbar_layer->opacity());
     EXPECT_FLOAT_EQ(0.f, pending_tree_node->data.opacity);
+    pending_scrollbar_layer->SetNeedsPushProperties();

[ajuma, 2016/05/18 13:53:48]

Is this line needed?

[jaydasika, 2016/05/19 00:27:09]

I added this when I realized ScrollbarlayerImplBase::PushPropertiesTo was not
getting called during the activation here. So, scrollbar_layer->opacity() was
not really getting tested. The active opacity remains because we don't push
properties and not because PushPropertiesTo ensures it. But, given that we are
going to delete LayerImpl::opacity soon, I think its not needed.

     host_impl_->ActivateSyncTree();
     active_tree_node =
         host_impl_->active_tree()->property_trees()->effect_tree.Node(