Mozart: Directly associate the renderer with the view tree.

services/gfx/compositor/renderer_state.cc

 // Copyright 2015 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 "services/gfx/compositor/renderer_state.h"
 
 #include "base/logging.h"
 #include "base/strings/stringprintf.h"
 
 namespace compositor {
 
 RendererState::RendererState(uint32_t id, const std::string& label)
     : id_(id), label_(label), weak_factory_(this) {}
 
 RendererState::~RendererState() {}
 
 bool RendererState::SetRootScene(SceneState* scene,
                                  uint32_t version,
                                  const mojo::Rect& viewport) {
   DCHECK(scene);
-  DCHECK(version);
 
   if (root_scene_ != scene || root_scene_version_ != version ||
       !root_scene_viewport_.Equals(viewport)) {
     root_scene_ = scene;
     root_scene_version_ = version;
     root_scene_viewport_ = viewport;
     SetSnapshot(nullptr);
     return true;
   }
   return false;
 }
 
+bool RendererState::ResetRootScene() {
+  if (root_scene_) {
+    root_scene_ = nullptr;
+    SetSnapshot(nullptr);
+    return true;
+  }
+  return false;
+}
+
 bool RendererState::SetSnapshot(std::unique_ptr<Snapshot> snapshot) {
   snapshot_ = std::move(snapshot);
   if (snapshot_ && snapshot_->valid()) {
     frame_ = snapshot_->frame();
     DCHECK(frame_);
     return true;
   }
   return false;
 }
 
 std::string RendererState::FormattedLabel() {
   if (formatted_label_cache_.empty()) {
     formatted_label_cache_ =
         label_.empty() ? base::StringPrintf("<%d>", id_)
                        : base::StringPrintf("<%d:%s>", id_, label_.c_str());
   }
   return formatted_label_cache_;
 }
 
 std::ostream& operator<<(std::ostream& os, RendererState* renderer_state) {
   if (!renderer_state)
     return os << "null";
   return os << renderer_state->FormattedLabel();
 }
 
 }  // namespace compositor