Reland of cc : Make LayerImpl destruction independent of tree hierarchy

cc/trees/layer_tree_host_impl_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/layer_tree_host_impl.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <cmath>
@@ skipping 520 matching lines @@
   on_can_draw_state_changed_called_ = false;
 
   // Set up the root layer, which allows us to draw.
   SetupScrollAndContentsLayers(gfx::Size(100, 100));
   EXPECT_TRUE(host_impl_->CanDraw());
   EXPECT_TRUE(on_can_draw_state_changed_called_);
   on_can_draw_state_changed_called_ = false;
 
   // Toggle the root layer to make sure it toggles can_draw
   host_impl_->active_tree()->SetRootLayer(nullptr);
+  host_impl_->active_tree()->DetachLayers();
   EXPECT_FALSE(host_impl_->CanDraw());
   EXPECT_TRUE(on_can_draw_state_changed_called_);
   on_can_draw_state_changed_called_ = false;
 
   SetupScrollAndContentsLayers(gfx::Size(100, 100));
   EXPECT_TRUE(host_impl_->CanDraw());
   EXPECT_TRUE(on_can_draw_state_changed_called_);
   on_can_draw_state_changed_called_ = false;
 
   // Toggle the device viewport size to make sure it toggles can_draw.
@@ skipping 183 matching lines @@
 TEST_F(LayerTreeHostImplTest, ReplaceTreeWhileScrolling) {
   LayerImpl* scroll_layer = SetupScrollAndContentsLayers(gfx::Size(100, 100));
   host_impl_->SetViewportSize(gfx::Size(50, 50));
   DrawFrame();
 
   // We should not crash if the tree is replaced while we are scrolling.
   EXPECT_EQ(InputHandler::SCROLL_ON_IMPL_THREAD,
             host_impl_->ScrollBegin(BeginState(gfx::Point()).get(),
                                     InputHandler::WHEEL)
                 .thread);
-  host_impl_->active_tree()->ClearLayers();
+  host_impl_->active_tree()->DetachLayers();
 
   scroll_layer = SetupScrollAndContentsLayers(gfx::Size(100, 100));
 
   // We should still be scrolling, because the scrolled layer also exists in the
   // new tree.
   gfx::Vector2d scroll_delta(0, 10);
   host_impl_->ScrollBy(UpdateState(gfx::Point(), scroll_delta).get());
   host_impl_->ScrollEnd(EndState().get());
   std::unique_ptr<ScrollAndScaleSet> scroll_info =
       host_impl_->ProcessScrollDeltas();
@@ skipping 4582 matching lines @@
   host_impl_->active_tree()->SetRootLayer(std::move(root_ptr));
   host_impl_->active_tree()->SetViewportLayersFromIds(Layer::INVALID_ID, 1, 3,
                                                       Layer::INVALID_ID);
   host_impl_->active_tree()->DidBecomeActive();
   host_impl_->SetViewportSize(surface_size);
 
   // Draw one frame and then immediately rebuild the layer tree to mimic a tree
   // synchronization.
   SetNeedsRebuildPropertyTrees();
   DrawFrame();
-  host_impl_->active_tree()->ClearLayers();
+  host_impl_->active_tree()->DetachLayers();
   std::unique_ptr<LayerImpl> root_ptr2 =
       LayerImpl::Create(host_impl_->active_tree(), 4);
   std::unique_ptr<LayerImpl> root_clip2 =
       LayerImpl::Create(host_impl_->active_tree(), 5);
   std::unique_ptr<LayerImpl> root_scroll2 =
       CreateScrollableLayer(6, surface_size, root_clip2.get());
   root_scroll2->test_properties()->is_container_for_fixed_position_layers =
       true;
   root_clip2->AddChild(std::move(root_scroll2));
   root_clip2->test_properties()->force_render_surface = true;
@@ skipping 1990 matching lines @@
 
   LayerTreeHostImpl::FrameData frame;
   EXPECT_EQ(DRAW_SUCCESS, PrepareToDrawFrame(&frame));
   host_impl_->DrawLayers(&frame);
   host_impl_->DidDrawAllLayers(frame);
   host_impl_->SwapBuffers(frame);
 
   EXPECT_GT(context3d->NumTextures(), 0u);
 
   // Kill the layer tree.
-  host_impl_->active_tree()->SetRootLayer(
-      LayerImpl::Create(host_impl_->active_tree(), 100));
+  host_impl_->active_tree()->DetachLayers();
   // There should be no textures left in use after.
   EXPECT_EQ(0u, context3d->NumTextures());
 }
 
 class MockDrawQuadsToFillScreenContext : public TestWebGraphicsContext3D {
  public:
   MOCK_METHOD1(useProgram, void(GLuint program));
   MOCK_METHOD4(drawElements, void(GLenum mode,
                                   GLsizei count,
                                   GLenum type,
@@ skipping 3445 matching lines @@
 
   // Re-initialize with a software output surface.
   output_surface_ = FakeOutputSurface::CreateSoftware(
       base::WrapUnique(new SoftwareOutputDevice));
   host_impl_->InitializeRenderer(output_surface_.get());
   EXPECT_FALSE(host_impl_->use_gpu_rasterization());
 }
 
 }  // namespace
 }  // namespace cc