cc : Fix effect tree index bug in cc::LayerImpl::Opacity

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 72b431a63100516e18878d1195291782b1f6d7da..a2544658639c3d789214af745f0a266f00261026 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -2865,19 +2865,22 @@ class LayerTreeHostImplTestScrollbarOpacity : public LayerTreeHostImplTest {
                                              VERTICAL, 10, 0, false, true);
     scrollbar->test_properties()->opacity = 0.f;
     LayerImpl* scroll = host_impl_->pending_tree()->OuterViewportScrollLayer();
-    LayerImpl* root = host_impl_->pending_tree()->InnerViewportContainerLayer();
+    LayerImpl* container =
+        host_impl_->pending_tree()->InnerViewportContainerLayer();
     scrollbar->SetScrollLayerId(scroll->id());
-    root->AddChild(std::move(scrollbar));
+    container->AddChild(std::move(scrollbar));
     host_impl_->pending_tree()->PushPageScaleFromMainThread(1.f, 1.f, 1.f);
     host_impl_->pending_tree()->BuildPropertyTreesForTesting();
     host_impl_->ActivateSyncTree();
 
-    LayerImpl* scrollbar_layer = host_impl_->active_tree()->LayerById(400);
+    LayerImpl* active_scrollbar_layer =
+        host_impl_->active_tree()->LayerById(400);
 
     EffectNode* active_tree_node =
         host_impl_->active_tree()->property_trees()->effect_tree.Node(
-            scrollbar_layer->effect_tree_index());
-    EXPECT_FLOAT_EQ(scrollbar_layer->Opacity(), active_tree_node->data.opacity);
+            active_scrollbar_layer->effect_tree_index());
+    EXPECT_FLOAT_EQ(active_scrollbar_layer->Opacity(),
+                    active_tree_node->data.opacity);
 
     host_impl_->ScrollbarAnimationControllerForId(scroll->id())
         ->DidMouseMoveNear(0);
@@ -2886,21 +2889,31 @@ class LayerTreeHostImplTestScrollbarOpacity : public LayerTreeHostImplTest {
     host_impl_->ScrollBy(UpdateState(gfx::Point(), gfx::Vector2dF(0, 5)).get());
     host_impl_->ScrollEnd(EndState().get());
     host_impl_->CreatePendingTree();
+    // To test the case where the effect tree index of scrollbar layer changes,
+    // we force the container layer to create a render surface.
+    container = host_impl_->pending_tree()->InnerViewportContainerLayer();
+    container->test_properties()->force_render_surface = true;
+    container->SetBounds(gfx::Size(10, 10));
+    host_impl_->pending_tree()->property_trees()->needs_rebuild = true;
+    host_impl_->pending_tree()->BuildPropertyTreesForTesting();
+
+    LayerImpl* pending_scrollbar_layer =
+        host_impl_->pending_tree()->LayerById(400);
     EffectNode* pending_tree_node =
         host_impl_->pending_tree()->property_trees()->effect_tree.Node(
-            scrollbar_layer->effect_tree_index());
+            pending_scrollbar_layer->effect_tree_index());
     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(1.f, active_scrollbar_layer->Opacity());
     EXPECT_FLOAT_EQ(0.f, pending_tree_node->data.opacity);
     host_impl_->ActivateSyncTree();
     active_tree_node =
         host_impl_->active_tree()->property_trees()->effect_tree.Node(
-            scrollbar_layer->effect_tree_index());
+            active_scrollbar_layer->effect_tree_index());
     EXPECT_FLOAT_EQ(1.f, active_tree_node->data.opacity);
-    EXPECT_FLOAT_EQ(1.f, scrollbar_layer->Opacity());
+    EXPECT_FLOAT_EQ(1.f, active_scrollbar_layer->Opacity());
   }
 };