Clean LayerImpl's scroll offset callers in unit tests.

cc/trees/property_tree.h

 // 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.
 
 #ifndef CC_TREES_PROPERTY_TREE_H_
 #define CC_TREES_PROPERTY_TREE_H_
 
 #include <stddef.h>
 
 #include <unordered_map>
@@ skipping 558 matching lines @@
   typedef std::unordered_map<int, scoped_refptr<SyncedScrollOffset>>
       ScrollOffsetMap;
 
   gfx::ScrollOffset MaxScrollOffset(int scroll_node_id) const;
   gfx::Size scroll_clip_layer_bounds(int scroll_node_id) const;
   ScrollNode* CurrentlyScrollingNode();
   const ScrollNode* CurrentlyScrollingNode() const;
   void set_currently_scrolling_node(int scroll_node_id);
   gfx::Transform ScreenSpaceTransform(int scroll_node_id) const;
 
-  // synced_scroll_offset is supposed to be called by Layer/LayerImpl only
   SyncedScrollOffset* synced_scroll_offset(int layer_id);
+  const SyncedScrollOffset* synced_scroll_offset(int layer_id) const;
   void CollectScrollDeltas(ScrollAndScaleSet* scroll_info);
   void UpdateScrollOffsetMap(ScrollOffsetMap* new_scroll_offset_map,
                              LayerTreeImpl* layer_tree_impl);
   ScrollOffsetMap& scroll_offset_map();
   const ScrollOffsetMap& scroll_offset_map() const;
   void ApplySentScrollDeltasFromAbortedCommit();
   bool SetScrollOffset(int layer_id, const gfx::ScrollOffset& scroll_offset);
+  bool UpdateScrollOffsetBaseForTesting(int layer_id,
+                                        const gfx::ScrollOffset& offset);
+  const gfx::ScrollOffset GetScrollOffsetBaseForTesting(int layer_id) const;
 
  private:
   int currently_scrolling_node_id_;
   ScrollOffsetMap layer_id_to_scroll_offset_map_;
 
   gfx::ScrollOffset PullDeltaForMainThread(SyncedScrollOffset* scroll_offset);
   void UpdateScrollOffsetMapEntry(int key,
                                   ScrollOffsetMap* new_scroll_offset_map,
                                   LayerTreeImpl* layer_tree_impl);
 };
@@ skipping 51 matching lines @@
 
  private:
   gfx::Vector2dF inner_viewport_container_bounds_delta_;
   gfx::Vector2dF outer_viewport_container_bounds_delta_;
   gfx::Vector2dF inner_viewport_scroll_bounds_delta_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_PROPERTY_TREE_H_