Fix page zoom to be frame-centric for out-of-process frames.

third_party/WebKit/public/web/WebView.h

 /*
  * Copyright (C) 2009, 2010, 2011, 2012 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:
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  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 187 matching lines @@
     // of 300% and 50% of original size, respectively.  Only plugins use
     // non whole-numbers, since they might choose to have specific zoom level so
     // that fixed-width content is fit-to-page-width, for example.
     virtual double zoomLevel() = 0;
 
     // Changes the zoom level to the specified level, clamping at the limits
     // noted above, and returns the current zoom level after applying the
     // change.
     virtual double setZoomLevel(double) = 0;
 
+    // Sets the zoom level for the specified WebLocalFrame.

[alexmos, 2016/04/07 01:20:56]

nit: add "and its local descendants" or something like that, depending on how
your page-level message exploration goes and how this ends up being used.

[wjmaclean, 2016/04/07 12:55:36]

This disappears in the new patch.

+    virtual double setZoomLevelForFrame(WebLocalFrame*, double zoomLevel) = 0;
+
     // Updates the zoom limits for this view.
     virtual void zoomLimitsChanged(double minimumZoomLevel,
                                    double maximumZoomLevel) = 0;
 
     // Helper functions to convert between zoom level and zoom factor.  zoom
     // factor is zoom percent / 100, so 300% = 3.0.
     BLINK_EXPORT static double zoomLevelToZoomFactor(double zoomLevel);
     BLINK_EXPORT static double zoomFactorToZoomLevel(double factor);
 
     // Returns the current text zoom factor, where 1.0 is the normal size, > 1.0
@@ skipping 262 matching lines @@
     // context's ability to deal with that failure gracefully can be tested.
     virtual void forceNextDrawingBufferCreationToFail() = 0;
 
 protected:
     ~WebView() {}
 };
 
 } // namespace blink
 
 #endif