Reland of cc : Make LayerImpl destruction independent of tree hierarchy

cc/trees/tree_synchronizer_unittest.cc

 // Copyright 2011 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 "cc/trees/tree_synchronizer.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <set>
@@ skipping 208 matching lines @@
   TreeSynchronizer::SynchronizeTrees(layer_tree_root.get(),
                                      host_->active_tree());
   layer_impl_tree_root = host_->active_tree()->root_layer();
 
   ExpectTreesAreIdentical(layer_tree_root.get(), layer_impl_tree_root,
                           host_->active_tree());
 
   ASSERT_EQ(1u, layer_impl_destruction_list.size());
   EXPECT_EQ(second_layer_impl_id, layer_impl_destruction_list[0]);
 
-  host_->active_tree()->ClearLayers();
+  host_->active_tree()->DetachLayers();
 }
 
 // Constructs a very simple tree and checks that a stacking-order change is
 // tracked properly.
 TEST_F(TreeSynchronizerTest, SyncSimpleTreeAndTrackStackingOrderChange) {
   std::vector<int> layer_impl_destruction_list;
 
   // Set up the tree and sync once. child2 needs to be synced here, too, even
   // though we remove it to set up the intended scenario.
   scoped_refptr<Layer> layer_tree_root =
@@ skipping 25 matching lines @@
   ExpectTreesAreIdentical(layer_tree_root.get(), layer_impl_tree_root,
                           host_->active_tree());
 
   TreeSynchronizer::PushLayerProperties(layer_tree_root->layer_tree_host(),
                                         host_->active_tree());
 
   // Check that the impl thread properly tracked the change.
   EXPECT_FALSE(layer_impl_tree_root->LayerPropertyChanged());
   EXPECT_FALSE(layer_impl_tree_root->children()[0]->LayerPropertyChanged());
   EXPECT_TRUE(layer_impl_tree_root->children()[1]->LayerPropertyChanged());
-  host_->active_tree()->ClearLayers();
+  host_->active_tree()->DetachLayers();
 }
 
 TEST_F(TreeSynchronizerTest, SyncSimpleTreeAndProperties) {
   scoped_refptr<Layer> layer_tree_root = Layer::Create();
   layer_tree_root->AddChild(Layer::Create());
   layer_tree_root->AddChild(Layer::Create());
 
   host_->SetRootLayer(layer_tree_root);
 
   // Pick some random properties to set. The values are not important, we're
@@ skipping 78 matching lines @@
   // After another synchronize our trees should match and we should not have
   // destroyed any LayerImpls
   TreeSynchronizer::SynchronizeTrees(layer_tree_root.get(),
                                      host_->active_tree());
   layer_impl_tree_root = host_->active_tree()->root_layer();
   ExpectTreesAreIdentical(layer_tree_root.get(), layer_impl_tree_root,
                           host_->active_tree());
 
   EXPECT_EQ(0u, layer_impl_destruction_list.size());
 
-  host_->active_tree()->ClearLayers();
+  host_->active_tree()->DetachLayers();
 }
 
 // Constructs a very simple tree, synchronizes it, then synchronizes to a
 // totally new tree. All layers from the old tree should be deleted.
 TEST_F(TreeSynchronizerTest, SyncSimpleTreeThenDestroy) {
   std::vector<int> layer_impl_destruction_list;
 
   scoped_refptr<Layer> old_layer_tree_root =
       MockLayer::Create(&layer_impl_destruction_list);
   old_layer_tree_root->AddChild(
@@ skipping 94 matching lines @@
                           host_->active_tree());
 
   // Remove the replica mask.
   replica_layer_with_mask->SetMaskLayer(NULL);
   TreeSynchronizer::SynchronizeTrees(layer_tree_root.get(),
                                      host_->active_tree());
   layer_impl_tree_root = host_->active_tree()->root_layer();
   ExpectTreesAreIdentical(layer_tree_root.get(), layer_impl_tree_root,
                           host_->active_tree());
 
-  host_->active_tree()->ClearLayers();
+  host_->active_tree()->DetachLayers();
 }
 
 TEST_F(TreeSynchronizerTest, SynchronizeCurrentlyScrollingNode) {
   LayerTreeSettings settings;
   FakeLayerTreeHostImplClient client;
   FakeImplTaskRunnerProvider task_runner_provider;
   FakeRenderingStatsInstrumentation stats_instrumentation;
   TestSharedBitmapManager shared_bitmap_manager;
   TestTaskGraphRunner task_graph_runner;
   FakeLayerTreeHostImpl* host_impl = host_->host_impl();
@@ skipping 126 matching lines @@
   scroll_offset_map[scroll_layer->id()]->PullDeltaForMainThread();
   scroll_offset_map[scroll_layer->id()]->SetCurrent(gfx::ScrollOffset(40, 50));
   scroll_offset_map[scroll_layer->id()]->PushFromMainThread(
       gfx::ScrollOffset(100, 100));
   scroll_offset_map[scroll_layer->id()]->PushPendingToActive();
   EXPECT_TRUE(is_equal(scroll_offset_map, scroll_tree.scroll_offset_map()));
 }
 
 }  // namespace
 }  // namespace cc