Add dedicated windowToViewport method

third_party/WebKit/public/web/WebWidgetClient.h

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 166 matching lines @@
     virtual void onMouseDown(const WebNode& mouseDownNode) { }
 
     // Converts the |rect| from Blink's Viewport coordinates to the
     // coordinates in the native window used to display the content, in
     // DIP.  They're identical in tradional world, but will differ when
     // use-zoom-for-dsf feature is eanbled, and Viewport coordinates
     // becomes DSF times larger than window coordinates.
     // TODO(oshima): Update the comment when the migration is completed.
     virtual void convertViewportToWindow(WebRect* rect) {}
 
+    // Converts the |scalar| from the coordinates in native window in
+    // DIP to Blink's Viewport coordinates. They're identical in
+    // tradional world, but will differ when use-zoom-for-dsf feature
+    // is eanbled.  TODO(oshima): Update the comment when the
+    // migration is completed.
+    virtual float convertWindowToViewport(float scalar) { return scalar; }

[dgozman, 2016/01/23 00:38:38]

I think we should either make this symmetrical to |convertViewportToWindow| and
operate on WebRect, or call it |windowToViewportScaleFactor| and let clients
multiply themselves as some of them already do.

+
 protected:
     ~WebWidgetClient() { }
 };
 
 } // namespace blink
 
 #endif