Made layout viewport scroll updates from compositor work like ordinary layers.

cc/trees/property_tree.cc

 // Copyright 2014 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.
 
 #include <stddef.h>
 
 #include <set>
 #include <vector>
 
 #include "base/logging.h"
@@ skipping 1271 matching lines @@
   gfx::ScrollOffset floored_delta(floor(current_delta.x()),
                                   floor(current_delta.y()));
   gfx::ScrollOffset diff_delta = floored_delta - current_delta;
   gfx::ScrollOffset tmp_offset = current_offset + diff_delta;
   scroll_offset->SetCurrent(tmp_offset);
   gfx::ScrollOffset delta = scroll_offset->PullDeltaForMainThread();
   scroll_offset->SetCurrent(current_offset);
   return delta;
 }
 
-void ScrollTree::CollectScrollDeltas(ScrollAndScaleSet* scroll_info) {
+void ScrollTree::CollectScrollDeltas(ScrollAndScaleSet* scroll_info,
+                                     int inner_viewport_layer_id) {
   for (auto map_entry : layer_id_to_scroll_offset_map_) {
     gfx::ScrollOffset scroll_delta =
         PullDeltaForMainThread(map_entry.second.get());
 
+    gfx::Vector2d scroll_delta_vector(scroll_delta.x(), scroll_delta.y());
+    int layer_id = map_entry.first;
+
     if (!scroll_delta.IsZero()) {
-      LayerTreeHostCommon::ScrollUpdateInfo scroll;
-      scroll.layer_id = map_entry.first;
-      scroll.scroll_delta = gfx::Vector2d(scroll_delta.x(), scroll_delta.y());
-      scroll_info->scrolls.push_back(scroll);
+      if (layer_id == inner_viewport_layer_id) {
+        // Inner (visual) viewport is stored separately.
+        scroll_info->inner_viewport_scroll.layer_id = layer_id;
+        scroll_info->inner_viewport_scroll.scroll_delta = scroll_delta_vector;
+      } else {
+        LayerTreeHostCommon::ScrollUpdateInfo scroll;
+        scroll.layer_id = layer_id;
+        scroll.scroll_delta = scroll_delta_vector;
+        scroll_info->scrolls.push_back(scroll);
+      }
     }
   }
 }
 
 void ScrollTree::CollectScrollDeltasForTesting() {
   for (auto map_entry : layer_id_to_scroll_offset_map_) {
     PullDeltaForMainThread(map_entry.second.get());
   }
 }
 
@@ skipping 572 matching lines @@
   cached_data_.property_tree_update_number = 0;
   cached_data_.animation_scales = std::vector<AnimationScaleData>(
       transform_tree.nodes().size(), AnimationScaleData());
 }
 
 void PropertyTrees::UpdateCachedNumber() {
   cached_data_.property_tree_update_number++;
 }
 
 }  // namespace cc