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 529 matching lines @@
   EXPECT_TRUE(layer_tree_impl->IsPendingTree());
   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.
   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);

[jaydasika, 2016/05/20 22:46:33]

This tests that 0 opacity gets pushed onto the active tree.

 }
 
 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