Add map from element id to scroll node index.

Essentially a scroll node specific version of
http://crrev.com/2612093002 which was only omitted there
in the interest of incrementality.

BUG=674258
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Review-Url: https://codereview.chromium.org/2623313003
Cr-Commit-Position: refs/heads/master@{#443348}

cc/trees/layer_tree_host_impl.cc

@@ -3948,16 +3948,14 @@ void LayerTreeHostImpl::SetTreeLayerScrollOffsetMutated(
       1u, property_trees->element_id_to_transform_node_index.count(element_id));
   int transform_node_index =
       property_trees->element_id_to_transform_node_index[element_id];
-  // TODO(wkorman): Build map from element id to scroll node in property tree
-  // builder and make use of it below.
+  DCHECK_EQ(1u,
+            property_trees->element_id_to_scroll_node_index.count(element_id));
   const int scroll_node_index =
-      property_trees->layer_id_to_scroll_node_index[layer_id];
-  if (scroll_node_index != ScrollTree::kInvalidNodeId) {
-    property_trees->scroll_tree.OnScrollOffsetAnimated(
-        layer_id, transform_node_index, scroll_node_index, scroll_offset, tree);
-    // Run mutation callbacks to respond to updated scroll offset.
-    Mutate(CurrentBeginFrameArgs().frame_time);
-  }
+      property_trees->element_id_to_scroll_node_index[element_id];
+  property_trees->scroll_tree.OnScrollOffsetAnimated(
+      layer_id, transform_node_index, scroll_node_index, scroll_offset, tree);
+  // Run mutation callbacks to respond to updated scroll offset.
+  Mutate(CurrentBeginFrameArgs().frame_time);
 }
 
 bool LayerTreeHostImpl::AnimationsPreserveAxisAlignment(

cc/trees/layer_tree_host_unittest.cc

@@ -57,6 +57,7 @@
 #include "cc/trees/layer_tree_host_common.h"
 #include "cc/trees/layer_tree_host_impl.h"
 #include "cc/trees/layer_tree_impl.h"
+#include "cc/trees/scroll_node.h"
 #include "cc/trees/single_thread_proxy.h"
 #include "cc/trees/swap_promise_manager.h"
 #include "cc/trees/transform_node.h"
@@ -943,9 +944,13 @@ class LayerTreeHostTestPushElementIdToNodeIdMap : public LayerTreeHostTest {
     switch (layer_tree_host()->SourceFrameNumber()) {
       case 1:
         child_->SetForceRenderSurfaceForTesting(true);
+        child_->AddMainThreadScrollingReasons(
+            MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects);
         break;
       case 2:
         child_->SetForceRenderSurfaceForTesting(false);
+        child_->ClearMainThreadScrollingReasons(
+            MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects);
         break;
     }
   }
@@ -961,12 +966,18 @@ class LayerTreeHostTestPushElementIdToNodeIdMap : public LayerTreeHostTest {
         EXPECT_EQ(2U, child_impl_->layer_tree_impl()
                           ->property_trees()
                           ->effect_tree.size());
+        EXPECT_EQ(2U, child_impl_->layer_tree_impl()
+                          ->property_trees()
+                          ->scroll_tree.size());
         EXPECT_TRUE(property_trees->element_id_to_transform_node_index.find(
                         kTestElementId) ==
                     property_trees->element_id_to_transform_node_index.end());
         EXPECT_TRUE(property_trees->element_id_to_effect_node_index.find(
                         kTestElementId) ==
                     property_trees->element_id_to_effect_node_index.end());
+        EXPECT_TRUE(property_trees->element_id_to_scroll_node_index.find(
+                        kTestElementId) ==
+                    property_trees->element_id_to_scroll_node_index.end());
         break;
       case 1:
         EXPECT_EQ(3U, child_impl_->layer_tree_impl()
@@ -975,11 +986,16 @@ class LayerTreeHostTestPushElementIdToNodeIdMap : public LayerTreeHostTest {
         EXPECT_EQ(3U, child_impl_->layer_tree_impl()
                           ->property_trees()
                           ->effect_tree.size());
+        EXPECT_EQ(3U, child_impl_->layer_tree_impl()
+                          ->property_trees()
+                          ->scroll_tree.size());
         EXPECT_EQ(
             2,
             property_trees->element_id_to_transform_node_index[kTestElementId]);
         EXPECT_EQ(
             2, property_trees->element_id_to_effect_node_index[kTestElementId]);
+        EXPECT_EQ(
+            2, property_trees->element_id_to_scroll_node_index[kTestElementId]);
         break;
       case 2:
         EXPECT_EQ(2U, child_impl_->layer_tree_impl()
@@ -994,6 +1010,9 @@ class LayerTreeHostTestPushElementIdToNodeIdMap : public LayerTreeHostTest {
         EXPECT_TRUE(property_trees->element_id_to_effect_node_index.find(
                         kTestElementId) ==
                     property_trees->element_id_to_effect_node_index.end());
+        EXPECT_TRUE(property_trees->element_id_to_scroll_node_index.find(
+                        kTestElementId) ==
+                    property_trees->element_id_to_scroll_node_index.end());
         break;
     }
     EndTest();

cc/trees/property_tree.cc

@@ -1566,6 +1566,8 @@ bool PropertyTrees::operator==(const PropertyTrees& other) const {
          layer_id_to_scroll_node_index == other.layer_id_to_scroll_node_index &&
          element_id_to_effect_node_index ==
              other.element_id_to_effect_node_index &&
+         element_id_to_scroll_node_index ==
+             other.element_id_to_scroll_node_index &&
          element_id_to_transform_node_index ==
              other.element_id_to_transform_node_index &&
          always_use_active_tree_opacity_effect_ids ==
@@ -1590,6 +1592,7 @@ PropertyTrees& PropertyTrees::operator=(const PropertyTrees& from) {
   layer_id_to_clip_node_index = from.layer_id_to_clip_node_index;
   layer_id_to_scroll_node_index = from.layer_id_to_scroll_node_index;
   element_id_to_effect_node_index = from.element_id_to_effect_node_index;
+  element_id_to_scroll_node_index = from.element_id_to_scroll_node_index;
   element_id_to_transform_node_index = from.element_id_to_transform_node_index;
   needs_rebuild = from.needs_rebuild;
   changed = from.changed;
@@ -1622,6 +1625,7 @@ void PropertyTrees::clear() {
   layer_id_to_clip_node_index.clear();
   layer_id_to_scroll_node_index.clear();
   element_id_to_effect_node_index.clear();
+  element_id_to_scroll_node_index.clear();
   element_id_to_transform_node_index.clear();
   always_use_active_tree_opacity_effect_ids.clear();
 

cc/trees/property_tree.h

@@ -571,6 +571,8 @@ class CC_EXPORT PropertyTrees final {
   // to produce cc property trees and these maps.
   std::unordered_map<ElementId, int, ElementIdHash>
       element_id_to_effect_node_index;
+  std::unordered_map<ElementId, int, ElementIdHash>
+      element_id_to_scroll_node_index;
   std::unordered_map<ElementId, int, ElementIdHash>
       element_id_to_transform_node_index;
 

cc/trees/property_tree_builder.cc

@@ -1158,8 +1158,10 @@ void AddScrollNodeIfNeeded(
         data_from_ancestor
             .scroll_tree_parent_created_by_uninheritable_criteria));
 
+  int node_id;
   if (!requires_node) {
-    data_for_children->scroll_tree_parent = parent_id;
+    node_id = parent_id;
+    data_for_children->scroll_tree_parent = node_id;
   } else {
     ScrollNode node;
     node.owning_layer_id = layer->id();
@@ -1194,15 +1196,21 @@ void AddScrollNodeIfNeeded(
     node.transform_id =
         data_for_children->transform_tree_parent->transform_tree_index();
 
-    data_for_children->scroll_tree_parent =
+    node_id =
         data_for_children->property_trees->scroll_tree.Insert(node, parent_id);
+    data_for_children->scroll_tree_parent = node_id;
     data_for_children->main_thread_scrolling_reasons =
         node.main_thread_scrolling_reasons;
     data_for_children->scroll_tree_parent_created_by_uninheritable_criteria =
         scroll_node_uninheritable_criteria;
     data_for_children->property_trees
-        ->layer_id_to_scroll_node_index[layer->id()] =
-        data_for_children->scroll_tree_parent;
+        ->layer_id_to_scroll_node_index[layer->id()] = node_id;
+    // For animation subsystem purposes, if this layer has a compositor element
+    // id, we build a map from that id to this scroll node.
+    if (layer->element_id()) {
+      data_for_children->property_trees
+          ->element_id_to_scroll_node_index[layer->element_id()] = node_id;
+    }
 
     if (node.scrollable) {
       data_for_children->property_trees->scroll_tree.SetBaseScrollOffset(
@@ -1210,7 +1218,7 @@ void AddScrollNodeIfNeeded(
     }
   }
 
-  layer->SetScrollTreeIndex(data_for_children->scroll_tree_parent);
+  layer->SetScrollTreeIndex(node_id);
 }
 
 template <typename LayerType>