Harmonize LayerTreeHost/LayerTreeHostImpl synchronization steps

cc/trees/layer_tree_impl.h

 // Copyright 2012 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.
 
 #ifndef CC_TREES_LAYER_TREE_IMPL_H_
 #define CC_TREES_LAYER_TREE_IMPL_H_
 
 #include <map>
 #include <set>
 #include <string>
@@ skipping 36 matching lines @@
 class ResourceProvider;
 class TileManager;
 class UIResourceRequest;
 class VideoFrameControllerClient;
 struct PendingPageScaleAnimation;
 
 typedef std::vector<UIResourceRequest> UIResourceRequestQueue;
 typedef SyncedProperty<AdditionGroup<float>> SyncedBrowserControls;
 typedef SyncedProperty<AdditionGroup<gfx::Vector2dF>> SyncedElasticOverscroll;
 
+class LayerTreeLifecycle {
+ public:
+  enum LifecycleState {
+    kNotSyncing,
+
+    // The following states are the steps performed when syncing properties to
+    // this tree (see: LayerTreeHost::FinishCommitOnImplThread or
+    // LayerTreeHostImpl::ActivateSyncTree).
+    kBeginningSync,
+    kSyncedPropertyTrees,
+    kSyncedLayerProperties,
+    kLastSyncState = kSyncedLayerProperties,
+
+    // TODO(pdr): Add states to cover more than just the synchronization steps.
+  };
+
+  void AdvanceTo(LifecycleState);
+
+  bool AllowsPropertyTreeAccess() const {
+    return state_ == kNotSyncing || state_ >= kSyncedPropertyTrees;
+  }
+  bool AllowsLayerPropertyAccess() const {
+    return state_ == kNotSyncing || state_ >= kSyncedLayerProperties;
+  }
+
+ private:
+  LifecycleState state_ = kNotSyncing;
+};
+
 class CC_EXPORT LayerTreeImpl {
  public:
   // This is the number of times a fixed point has to be hit continuously by a
   // layer to consider it as jittering.
   enum : int { kFixedPointHitsThreshold = 3 };
   LayerTreeImpl(LayerTreeHostImpl* layer_tree_host_impl,
                 scoped_refptr<SyncedProperty<ScaleGroup>> page_scale_factor,
                 scoped_refptr<SyncedBrowserControls> top_controls_shown_ratio,
                 scoped_refptr<SyncedElasticOverscroll> elastic_overscroll);
   virtual ~LayerTreeImpl();
@@ skipping 56 matching lines @@
     return layer_list_.empty() ? nullptr : layer_list_[0];
   }
   const RenderSurfaceImpl* RootRenderSurface() const;
   bool LayerListIsEmpty() const;
   void SetRootLayerForTesting(std::unique_ptr<LayerImpl>);
   void OnCanDrawStateChangedForTree();
   bool IsRootLayer(const LayerImpl* layer) const;
   std::unique_ptr<OwnedLayerImplList> DetachLayers();
 
   void SetPropertyTrees(PropertyTrees* property_trees);
-  PropertyTrees* property_trees() { return &property_trees_; }
+  PropertyTrees* property_trees() {
+    // TODO(pdr): We should enable this DCHECK because it will catch uses of
+    // stale property trees, but it currently fails too many existing tests.
+    // DCHECK(lifecycle().AllowsPropertyTreeAccess());
+    return &property_trees_;
+  }
 
+  void PushPropertyTreesTo(LayerTreeImpl* tree_impl);
   void PushPropertiesTo(LayerTreeImpl* tree_impl);
 
   void MoveChangeTrackingToLayers();
 
   void ForceRecalculateRasterScales();
 
   LayerImplList::const_iterator begin() const;
   LayerImplList::const_iterator end() const;
   LayerImplList::reverse_iterator rbegin();
   LayerImplList::reverse_iterator rend();
@@ skipping 315 matching lines @@
 
   void AddToLayerList(LayerImpl* layer);
 
   void ClearLayerList();
 
   void BuildLayerListForTesting();
   void HandleScrollbarShowRequestsFromMain();
 
   void InvalidateRegionForImages(const ImageIdFlatSet& images_to_invalidate);
 
+  LayerTreeLifecycle& lifecycle() { return lifecycle_; }
+
  protected:
   float ClampPageScaleFactorToLimits(float page_scale_factor) const;
   void PushPageScaleFactorAndLimits(const float* page_scale_factor,
                                     float min_page_scale_factor,
                                     float max_page_scale_factor);
   bool SetPageScaleFactorLimits(float min_page_scale_factor,
                                 float max_page_scale_factor);
   bool IsViewportLayerId(int id) const;
   void UpdateScrollbars(int scroll_layer_id, int clip_layer_id);
   void DidUpdatePageScale();
@@ skipping 94 matching lines @@
   bool browser_controls_shrink_blink_size_;
   float top_controls_height_;
   float bottom_controls_height_;
 
   // The amount that the browser controls are shown from 0 (hidden) to 1 (fully
   // shown).
   scoped_refptr<SyncedBrowserControls> top_controls_shown_ratio_;
 
   std::unique_ptr<PendingPageScaleAnimation> pending_page_scale_animation_;
 
+  // Tracks the lifecycle which is used for enforcing dependencies between
+  // lifecycle states. See: |LayerTreeLifecycle|.
+  LayerTreeLifecycle lifecycle_;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_