gfx: Make conversions from Size to SizeF be explicit.

cc/input/input_handler.h

 // Copyright 2011 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_INPUT_INPUT_HANDLER_H_
 #define CC_INPUT_INPUT_HANDLER_H_
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
 #include "cc/base/cc_export.h"
 #include "cc/input/scrollbar.h"
 #include "cc/trees/swap_promise_monitor.h"
 
 namespace gfx {
 class Point;
 class PointF;
 class ScrollOffset;
+class SizeF;
 class Vector2d;
 class Vector2dF;
 }
 
 namespace ui {
 class LatencyInfo;
 }
 
 namespace cc {
 
@@ skipping 149 matching lines @@
   InputHandler() {}
   virtual ~InputHandler() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(InputHandler);
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_INPUT_HANDLER_H_