cc : Initialize solid color scrollbar layer on main thread to 0.

cc/layers/scrollbar_layer_unittest.cc

 // Copyright 2012 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 <stddef.h>
 
 #include <unordered_map>
 
 #include "base/threading/thread_task_runner_handle.h"
 #include "cc/input/scrollbar_animation_controller.h"
@@ skipping 504 matching lines @@
   scrollbar_layer->ToScrollbarLayer()->SetScrollLayer(scroll_layer->id());
   scroll_layer->AddChild(child1);
   scroll_layer->InsertChild(scrollbar_layer, 1);
   layer_tree_root->AddChild(scroll_layer);
   layer_tree_host_->SetRootLayer(layer_tree_root);
 
   // Choose layer bounds to give max_scroll_offset = (8, 8).
   layer_tree_root->SetBounds(gfx::Size(2, 2));
   scroll_layer->SetBounds(gfx::Size(10, 10));
 
-  layer_tree_host_->UpdateLayers();
-
-  LayerImpl* layer_impl_tree_root =
-      layer_tree_host_->CommitAndCreateLayerImplTree();
-
-  scrollbar_layer->SetOpacity(0.5f);
+  // A solid color scrollbar layer's opacity is initialized to 0 on main thread
   layer_tree_host_->UpdateLayers();
   EffectNode* node = layer_tree_host_->property_trees()->effect_tree.Node(
       scrollbar_layer->effect_tree_index());
-  EXPECT_EQ(node->data.opacity, 0.5f);
+  EXPECT_EQ(node->data.opacity, 0.f);
 
+  // This tests that the initial opacity(0) of the scrollbar gets pushed onto
+  // the pending tree and then onto the active tree.
   LayerTreeHostImpl* host_impl = layer_tree_host_->host_impl();
   host_impl->CreatePendingTree();
-  layer_impl_tree_root = layer_tree_host_->CommitAndCreatePendingTree();
+  LayerImpl* layer_impl_tree_root =
+      layer_tree_host_->CommitAndCreatePendingTree();
   LayerTreeImpl* layer_tree_impl = layer_impl_tree_root->layer_tree_impl();
   EXPECT_TRUE(layer_tree_impl->IsPendingTree());
-  layer_tree_impl->property_trees()->effect_tree.Node(
+  node = layer_tree_impl->property_trees()->effect_tree.Node(
       scrollbar_layer->effect_tree_index());
-  EXPECT_EQ(node->data.opacity, 0.5f);
-  // The active tree opacity should not change with activation for scrollbar
-  // layer.
+  EXPECT_EQ(node->data.opacity, 0.f);
   host_impl->ActivateSyncTree();
   layer_tree_impl = host_impl->active_tree();
   node = layer_tree_impl->property_trees()->effect_tree.Node(
       scrollbar_layer->effect_tree_index());
-  EXPECT_EQ(node->data.opacity, 1.f);
+  EXPECT_EQ(node->data.opacity, 0.f);
+
+  // This tests that activation does not change the opacity of scrollbar layer.
+  LayerImpl* scrollbar_layer_impl =
+      layer_tree_impl->LayerById(scrollbar_layer->id());
+  scrollbar_layer_impl->OnOpacityAnimated(0.25f);
+  host_impl->CreatePendingTree();
+  layer_impl_tree_root = layer_tree_host_->CommitAndCreatePendingTree();
+  layer_tree_impl = layer_impl_tree_root->layer_tree_impl();
+  EXPECT_TRUE(layer_tree_impl->IsPendingTree());
+  node = layer_tree_impl->property_trees()->effect_tree.Node(
+      scrollbar_layer->effect_tree_index());
+  EXPECT_EQ(node->data.opacity, 0.f);
+  host_impl->ActivateSyncTree();
+  layer_tree_impl = host_impl->active_tree();
+  node = layer_tree_impl->property_trees()->effect_tree.Node(
+      scrollbar_layer->effect_tree_index());
+  EXPECT_EQ(node->data.opacity, 0.25f);
 }
 
 class ScrollbarLayerSolidColorThumbTest : public testing::Test {
  public:
   ScrollbarLayerSolidColorThumbTest() {
     LayerTreeSettings layer_tree_settings;
     host_impl_.reset(new FakeLayerTreeHostImpl(
         layer_tree_settings, &task_runner_provider_, &shared_bitmap_manager_,
         &task_graph_runner_));
 
@@ skipping 511 matching lines @@
   TestScale(gfx::Rect(1240, 0, 15, 1333), 2.7754839f);
   TestScale(gfx::Rect(1240, 0, 15, 677), 2.46677136f);
 
   // Horizontal Scrollbars.
   TestScale(gfx::Rect(0, 1240, 1333, 15), 2.7754839f);
   TestScale(gfx::Rect(0, 1240, 677, 15), 2.46677136f);
 }
 
 }  // namespace
 }  // namespace cc