Fixed position layer counter-scroll with main thread scroll offset fractional part

cc/layers/layer.h

 // Copyright 2010 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_LAYERS_LAYER_H_
 #define CC_LAYERS_LAYER_H_
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 299 matching lines @@
     return draw_checkerboard_for_missing_tiles_;
   }
 
   void SetForceRenderSurface(bool force_render_surface);
   bool force_render_surface() const { return force_render_surface_; }
 
   gfx::Vector2dF ScrollDelta() const { return gfx::Vector2dF(); }
   gfx::ScrollOffset TotalScrollOffset() const {
     return ScrollOffsetWithDelta(scroll_offset(), ScrollDelta());
   }
+  gfx::Vector2dF MainScrollOffsetFracitionalPart() const {
+    return scroll_offset_fractional_part_;
+  }
 
   void SetDoubleSided(bool double_sided);
   bool double_sided() const { return double_sided_; }
 
   void SetShouldFlattenTransform(bool flatten);
   bool should_flatten_transform() const { return should_flatten_transform_; }
 
   bool Is3dSorted() const { return sorting_context_id_ != 0; }
 
   void set_use_parent_backface_visibility(bool use) {
@@ skipping 299 matching lines @@
   // This pointer value is nil when a Layer is not in a tree and is
   // updated via SetLayerTreeHost() if a layer moves between trees.
   LayerTreeHost* layer_tree_host_;
 
   scoped_refptr<LayerAnimationController> layer_animation_controller_;
 
   // Layer properties.
   gfx::Size bounds_;
 
   gfx::ScrollOffset scroll_offset_;
+  gfx::Vector2dF scroll_offset_fractional_part_;
   // This variable indicates which ancestor layer (if any) whose size,
   // transformed relative to this layer, defines the maximum scroll offset for
   // this layer.
   int scroll_clip_layer_id_;
   int num_descendants_that_draw_content_;
   int transform_tree_index_;
   int opacity_tree_index_;
   int clip_tree_index_;
   gfx::Vector2dF offset_to_transform_parent_;
   bool should_scroll_on_main_thread_ : 1;
@@ skipping 56 matching lines @@
 
   std::vector<FrameTimingRequest> frame_timing_requests_;
   bool frame_timing_requests_dirty_;
 
   DISALLOW_COPY_AND_ASSIGN(Layer);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_H_