Fix viewport computation in Mac UC

cc/output/compositor_frame_metadata.h

 // Copyright (c) 2012 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_OUTPUT_COMPOSITOR_FRAME_METADATA_H_
 #define CC_OUTPUT_COMPOSITOR_FRAME_METADATA_H_
 
 #include <vector>
 
 #include "cc/base/cc_export.h"
@@ skipping 12 matching lines @@
   // The device scale factor used to generate this compositor frame.
   float device_scale_factor;
 
   // Scroll offset and scale of the root layer. This can be used for tasks
   // like positioning windowed plugins.
   gfx::Vector2dF root_scroll_offset;
   float page_scale_factor;
 
   // These limits can be used together with the scroll/scale fields above to
   // determine if scrolling/scaling in a particular direction is possible.
-  gfx::SizeF viewport_size;
+  gfx::SizeF scrollable_viewport_size;
   gfx::SizeF root_layer_size;
   float min_page_scale_factor;
   float max_page_scale_factor;
 
   // Used to position the Android location top bar and page content, whose
   // precise position is computed by the renderer compositor.
   gfx::Vector2dF location_bar_offset;
   gfx::Vector2dF location_bar_content_translation;
   float overdraw_bottom_height;
 
   // Provides selection region updates relative to the current viewport. If the
   // selection is empty or otherwise unused, the bound types will indicate such.
   ViewportSelectionBound selection_anchor;
   ViewportSelectionBound selection_focus;
 
   std::vector<ui::LatencyInfo> latency_info;
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_COMPOSITOR_FRAME_METADATA_H_