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 33e17df36dbcd6eccc72e0f565d7195437c20185..260ce711a3537727afd7a4b7c2d85ec534bf39ea 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;
+#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.