Add a cache of LayerImpl's viewport layer type

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 1fe5871b8a0bc4da2f26728082415c94c7f2dd51..3be9697d152c355ac50d96c76049364621ae5c83 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -139,16 +139,24 @@ void LayerTreeImpl::RecreateTileResources() {
 }
 
 bool LayerTreeImpl::IsViewportLayerId(int id) const {
-  if (id == inner_viewport_scroll_layer_id_ ||
-      id == outer_viewport_scroll_layer_id_)
-    return true;

[jaydasika, 2017/05/09 05:54:22]

Since we want to avoid calling LayerById whenever possible (as its costly), can
we keep this ? 

[pdr., 2017/05/09 22:20:07]

I'm a little torn on this because I don't know the most common way this function
is called. For example, if inner_viewport_scroll_layer_id_ or
outer_viewport_scroll_layer_id_ equal the id, your suggestion will be fast. On
the other hand, the old InnerViewportContainerLayer() and
OuterViewportContainerLayer() conditionals actually had two LayerById() calls in
them, so the new code would be faster. WDYT of committing this and seeing the
effect on the perf graphs?

[jaydasika, 2017/05/09 22:55:11]

Sounds good. lets commit this and see the perf graphs.

+#if DCHECK_IS_ON()
+  // Ensure the LayerImpl viewport layer types correspond to the LayerTreeImpl's
+  // viewport layers.
+  if (id == inner_viewport_scroll_layer_id_)
+    DCHECK(LayerById(id)->viewport_layer_type() == INNER_VIEWPORT_SCROLL);
+  if (id == outer_viewport_scroll_layer_id_)
+    DCHECK(LayerById(id)->viewport_layer_type() == OUTER_VIEWPORT_SCROLL);
   if (InnerViewportContainerLayer() &&
       id == InnerViewportContainerLayer()->id())
-    return true;
+    DCHECK(InnerViewportContainerLayer()->viewport_layer_type() ==
+           INNER_VIEWPORT_CONTAINER);
   if (OuterViewportContainerLayer() &&
       id == OuterViewportContainerLayer()->id())
-    return true;
-
+    DCHECK(OuterViewportContainerLayer()->viewport_layer_type() ==
+           OUTER_VIEWPORT_CONTAINER);
+#endif
+  if (auto* layer = LayerById(id))
+    return layer->viewport_layer_type() != NOT_VIEWPORT_LAYER;
   return false;
 }
 
@@ -410,6 +418,12 @@ void LayerTreeImpl::PushPropertiesTo(LayerTreeImpl* target_tree) {
   target_tree->set_bottom_controls_height(bottom_controls_height_);
   target_tree->PushBrowserControls(nullptr);
 
+  // The page scale factor update can affect scrolling which requires that
+  // these ids are set, so this must be before PushPageScaleFactorAndLimits.
+  target_tree->SetViewportLayersFromIds(
+      overscroll_elasticity_layer_id_, page_scale_layer_id_,
+      inner_viewport_scroll_layer_id_, outer_viewport_scroll_layer_id_);
+
   // Active tree already shares the page_scale_factor object with pending
   // tree so only the limits need to be provided.
   target_tree->PushPageScaleFactorAndLimits(nullptr, min_page_scale_factor(),
@@ -426,10 +440,6 @@ void LayerTreeImpl::PushPropertiesTo(LayerTreeImpl* target_tree) {
   target_tree->pending_page_scale_animation_ =
       std::move(pending_page_scale_animation_);
 
-  target_tree->SetViewportLayersFromIds(
-      overscroll_elasticity_layer_id_, page_scale_layer_id_,
-      inner_viewport_scroll_layer_id_, outer_viewport_scroll_layer_id_);
-
   target_tree->RegisterSelection(selection_);
 
   // This should match the property synchronization in
@@ -974,13 +984,26 @@ void LayerTreeImpl::SetViewportLayersFromIds(
   page_scale_layer_id_ = page_scale_layer_id;
   inner_viewport_scroll_layer_id_ = inner_viewport_scroll_layer_id;
   outer_viewport_scroll_layer_id_ = outer_viewport_scroll_layer_id;
+
+  UpdateViewportLayerTypes();
 }
 
 void LayerTreeImpl::ClearViewportLayers() {
-  overscroll_elasticity_layer_id_ = Layer::INVALID_ID;
-  page_scale_layer_id_ = Layer::INVALID_ID;
-  inner_viewport_scroll_layer_id_ = Layer::INVALID_ID;
-  outer_viewport_scroll_layer_id_ = Layer::INVALID_ID;
+  SetViewportLayersFromIds(Layer::INVALID_ID, Layer::INVALID_ID,
+                           Layer::INVALID_ID, Layer::INVALID_ID);
+}
+
+void LayerTreeImpl::UpdateViewportLayerTypes() {
+  if (auto* inner_scroll = LayerById(inner_viewport_scroll_layer_id_)) {
+    inner_scroll->SetViewportLayerType(INNER_VIEWPORT_SCROLL);
+    if (auto* inner_container = inner_scroll->scroll_clip_layer())
+      inner_container->SetViewportLayerType(INNER_VIEWPORT_CONTAINER);
+  }
+  if (auto* outer_scroll = LayerById(outer_viewport_scroll_layer_id_)) {
+    outer_scroll->SetViewportLayerType(OUTER_VIEWPORT_SCROLL);
+    if (auto* outer_container = outer_scroll->scroll_clip_layer())
+      outer_container->SetViewportLayerType(OUTER_VIEWPORT_CONTAINER);
+  }
 }
 
 // For unit tests, we use the layer's id as its element id.