[cc] Change semantics of fixed-pos container layer

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 <stddef.h>
 #include <stdint.h>
 
@@ skipping 200 matching lines @@
   }
 
   void SetScrollOffset(const gfx::ScrollOffset& scroll_offset);
 
   gfx::ScrollOffset scroll_offset() const { return inputs_.scroll_offset; }
   void SetScrollOffsetFromImplSide(const gfx::ScrollOffset& scroll_offset);
 
   void SetScrollClipLayerId(int clip_layer_id);
   bool scrollable() const { return inputs_.scroll_clip_layer_id != INVALID_ID; }
   Layer* scroll_clip_layer() const;
+  int scroll_clip_layer_id() const { return inputs_.scroll_clip_layer_id; }
 
   void SetUserScrollable(bool horizontal, bool vertical);
   bool user_scrollable_horizontal() const {
     return inputs_.user_scrollable_horizontal;
   }
   bool user_scrollable_vertical() const {
     return inputs_.user_scrollable_vertical;
   }
 
   void AddMainThreadScrollingReasons(uint32_t main_thread_scrolling_reasons);
@@ skipping 408 matching lines @@
   // These all act like draw properties, so don't need push properties.
   gfx::Rect visible_layer_rect_;
   size_t num_unclipped_descendants_;
 
   DISALLOW_COPY_AND_ASSIGN(Layer);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_H_