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

cc/layers/scrollbar_layer_unittest.cc

Index: cc/layers/scrollbar_layer_unittest.cc
diff --git a/cc/layers/scrollbar_layer_unittest.cc b/cc/layers/scrollbar_layer_unittest.cc
index 22114c8b297e714db75c1e5a206148c5ed3cb2fd..81b99f04dc83a05c73fcf1258bb38d49f0cce9e6 100644
--- a/cc/layers/scrollbar_layer_unittest.cc
+++ b/cc/layers/scrollbar_layer_unittest.cc
@@ -522,32 +522,45 @@ TEST_F(ScrollbarLayerTest, ScrollbarLayerOpacity) {
   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.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.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, 0.5f);
-  // 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, 0.25f);
 }
 
 class ScrollbarLayerSolidColorThumbTest : public testing::Test {