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

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 402a94ec3955b520b8f2caf9f2b6f00779e29798..77317ed68a1d99f1510064d7b820de7d98b361c5 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -2678,6 +2678,7 @@ class LayerTreeHostImplTestScrollbarAnimation : public LayerTreeHostImplTest {
     std::unique_ptr<SolidColorScrollbarLayerImpl> scrollbar =
         SolidColorScrollbarLayerImpl::Create(host_impl_->active_tree(), 400,
                                              VERTICAL, 10, 0, false, true);
+    scrollbar->SetOpacity(0.f);
     EXPECT_FLOAT_EQ(0.f, scrollbar->opacity());
 
     LayerImpl* scroll = host_impl_->active_tree()->OuterViewportScrollLayer();
@@ -2862,6 +2863,7 @@ class LayerTreeHostImplTestScrollbarOpacity : public LayerTreeHostImplTest {
     std::unique_ptr<SolidColorScrollbarLayerImpl> scrollbar =
         SolidColorScrollbarLayerImpl::Create(host_impl_->pending_tree(), 400,
                                              VERTICAL, 10, 0, false, true);
+    scrollbar->SetOpacity(0.f);
     LayerImpl* scroll = host_impl_->pending_tree()->OuterViewportScrollLayer();
     LayerImpl* root = host_impl_->pending_tree()->InnerViewportContainerLayer();
     scrollbar->SetScrollLayerId(scroll->id());