Convert element to layer map to just track elements in list.

The element_layers_map_ is only used to determine when elements are in
the active or pending tree for the purposes of ticking animations. This
patch converts the element layers map to a set tracking which element
ids are present.

Bug: 836897
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel;luci.chromium.try:linux-blink-gen-property-trees
Change-Id: I858a00d4f80fc5ac36a21e5d4cf21e0e379abdec
Reviewed-on: https://chromium-review.googlesource.com/1071072
Reviewed-by: Philip Rogers <pdr@chromium.org>
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Commit-Queue: Robert Flack <flackr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562286}

cc/layers/layer_impl.cc

@@ -84,15 +84,15 @@ LayerImpl::LayerImpl(LayerTreeImpl* tree_impl, int id)
 
   DCHECK(layer_tree_impl_);
   layer_tree_impl_->RegisterLayer(this);
-  layer_tree_impl_->AddToElementMap(this);
+  layer_tree_impl_->AddToElementLayerList(element_id_);
 
   SetNeedsPushProperties();
 }
 
 LayerImpl::~LayerImpl() {
   DCHECK_EQ(DRAW_MODE_NONE, current_draw_mode_);
   layer_tree_impl_->UnregisterLayer(this);
-  layer_tree_impl_->RemoveFromElementMap(this);
+  layer_tree_impl_->RemoveFromElementLayerList(element_id_);
   TRACE_EVENT_OBJECT_DELETED_WITH_ID(
       TRACE_DISABLED_BY_DEFAULT("cc.debug"), "cc::LayerImpl", this);
 }
@@ -643,9 +643,9 @@ void LayerImpl::SetElementId(ElementId element_id) {
   TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("cc.debug"), "LayerImpl::SetElementId",
                "element", element_id.AsValue().release());
 
-  layer_tree_impl_->RemoveFromElementMap(this);
+  layer_tree_impl_->RemoveFromElementLayerList(element_id_);
   element_id_ = element_id;
-  layer_tree_impl_->AddToElementMap(this);
+  layer_tree_impl_->AddToElementLayerList(element_id_);
 
   SetNeedsPushProperties();
 }

cc/layers/scrollbar_layer_unittest.cc

@@ -965,10 +965,6 @@ TEST_F(AuraScrollbarLayerTest, ScrollbarLayerCreateAfterSetScrollable) {
   layer_tree_host_->CommitAndCreatePendingTree();
   host_impl->ActivateSyncTree();
 
-  LayerImpl* scroll_layer_impl =
-      host_impl->active_tree()->LayerByElementId(scroll_layer->element_id());
-  EXPECT_TRUE(scroll_layer_impl->needs_show_scrollbars());
-
   std::unique_ptr<Scrollbar> scrollbar(new FakeScrollbar(false, true, true));
   scoped_refptr<Layer> scrollbar_layer = SolidColorScrollbarLayer::Create(
       scrollbar->Orientation(), kThumbThickness, kTrackStart,

cc/trees/layer_tree_host_impl.cc

@@ -5161,18 +5161,11 @@ bool LayerTreeHostImpl::ScrollAnimationUpdateTarget(
 
 bool LayerTreeHostImpl::IsElementInList(ElementId element_id,
                                         ElementListType list_type) const {
-  if (list_type == ElementListType::ACTIVE) {
-    return active_tree()
-               ? active_tree()->LayerByElementId(element_id) != nullptr
-               : false;
-  } else {
-    if (pending_tree() && pending_tree()->LayerByElementId(element_id))
-      return true;
-    if (recycle_tree() && recycle_tree()->LayerByElementId(element_id))
-      return true;
+  if (list_type == ElementListType::ACTIVE)
+    return active_tree() && active_tree()->IsElementInLayerList(element_id);
 
-    return false;
-  }
+  return (pending_tree() && pending_tree()->IsElementInLayerList(element_id)) ||
+         (recycle_tree() && recycle_tree()->IsElementInLayerList(element_id));
 }
 
 void LayerTreeHostImpl::SetMutatorsNeedCommit() {}

cc/trees/layer_tree_impl.cc

@@ -596,52 +596,47 @@ LayerImplList::reverse_iterator LayerTreeImpl::rend() {
   return layer_list_.rend();
 }
 
-LayerImpl* LayerTreeImpl::LayerByElementId(ElementId element_id) const {
-  auto iter = element_layers_map_.find(element_id);
-  return (iter == element_layers_map_.end()) ? nullptr
-                                             : LayerById(iter->second);
+bool LayerTreeImpl::IsElementInLayerList(ElementId element_id) const {
+  return elements_in_layer_list_.count(element_id);
 }
 
 ElementListType LayerTreeImpl::GetElementTypeForAnimation() const {
   return IsActiveTree() ? ElementListType::ACTIVE : ElementListType::PENDING;
 }
 
-void LayerTreeImpl::AddToElementMap(LayerImpl* layer) {
-  ElementId element_id = layer->element_id();
+void LayerTreeImpl::AddToElementLayerList(ElementId element_id) {
   if (!element_id)
     return;
 
-  TRACE_EVENT2(TRACE_DISABLED_BY_DEFAULT("layer-element"),
-               "LayerTreeImpl::AddToElementMap", "element",
-               element_id.AsValue().release(), "layer_id", layer->id());
+  TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("layer-element"),
+               "LayerTreeImpl::AddToElementLayerList", "element",
+               element_id.AsValue().release());
 
 #if DCHECK_IS_ON()
-  LayerImpl* existing_layer = LayerByElementId(element_id);
   bool element_id_collision_detected =
-      existing_layer && existing_layer != layer;
+      elements_in_layer_list_.count(element_id);
 
   DCHECK(!element_id_collision_detected);
 #endif
 
-  element_layers_map_[element_id] = layer->id();
+  elements_in_layer_list_.insert(element_id);
 
   host_impl_->mutator_host()->RegisterElement(element_id,
                                               GetElementTypeForAnimation());
 }
 
-void LayerTreeImpl::RemoveFromElementMap(LayerImpl* layer) {
-  if (!layer->element_id())
+void LayerTreeImpl::RemoveFromElementLayerList(ElementId element_id) {
+  if (!element_id)
     return;
 
-  TRACE_EVENT2(TRACE_DISABLED_BY_DEFAULT("layer-element"),
-               "LayerTreeImpl::RemoveFromElementMap", "element",
-               layer->element_id().AsValue().release(), "layer_id",
-               layer->id());
+  TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("layer-element"),
+               "LayerTreeImpl::RemoveFromElementLayerList", "element",
+               element_id.AsValue().release());
 
-  host_impl_->mutator_host()->UnregisterElement(layer->element_id(),
+  host_impl_->mutator_host()->UnregisterElement(element_id,
                                                 GetElementTypeForAnimation());
 
-  element_layers_map_.erase(layer->element_id());
+  elements_in_layer_list_.erase(element_id);
 }
 
 void LayerTreeImpl::SetTransformMutated(ElementId element_id,

cc/trees/layer_tree_impl.h

@@ -381,11 +381,9 @@ class CC_EXPORT LayerTreeImpl {
 
   LayerImpl* LayerById(int id) const;
 
-  // TODO(jaydasika): this is deprecated. It is used by
-  // scrolling animation to look up layers to mutate.
-  LayerImpl* LayerByElementId(ElementId element_id) const;
-  void AddToElementMap(LayerImpl* layer);
-  void RemoveFromElementMap(LayerImpl* layer);
+  bool IsElementInLayerList(ElementId element_id) const;
+  void AddToElementLayerList(ElementId element_id);
+  void RemoveFromElementLayerList(ElementId element_id);
 
   void SetSurfaceLayerIds(
       const base::flat_set<viz::SurfaceId>& surface_layer_ids);
@@ -622,7 +620,8 @@ class CC_EXPORT LayerTreeImpl {
   // Set of layers that need to push properties.
   std::unordered_set<LayerImpl*> layers_that_should_push_properties_;
 
-  std::unordered_map<ElementId, int, ElementIdHash> element_layers_map_;
+  // Set of ElementIds which are present in the |layer_list_|.
+  std::unordered_set<ElementId, ElementIdHash> elements_in_layer_list_;
 
   std::unordered_map<ElementId, float, ElementIdHash>
       element_id_to_opacity_animations_;