Make zoom filter independent of the layer size.

ui/compositor/layer.h

Index: ui/compositor/layer.h
diff --git a/ui/compositor/layer.h b/ui/compositor/layer.h
index e416e80dbb0b059274135d92b4083fcc35a9ddc5..80de3ccff586696168f88013fadc3e7f49eab64f 100644
--- a/ui/compositor/layer.h
+++ b/ui/compositor/layer.h
@@ -180,11 +180,9 @@ class COMPOSITOR_EXPORT Layer
   // grayscale otherwise.
   float GetTargetGrayscale() const;
 
-  // Zoom the background by a factor of |zoom|.  The upper left corner of the
-  // zoomed area is offset from the top left corner of the layer by |x_offset|
-  // and |y_offset|.  The effect is blended along the edge across |inset|
-  // pixels.
-  void SetBackgroundZoom(float x_offset, float y_offset, float zoom, int inset);
+  // Zoom the background by a factor of |zoom|. The effect is blended along the
+  // edge across |inset| pixels.
+  void SetBackgroundZoom(float zoom, int inset);
 
   // Invert the layer.
   bool layer_inverted() const { return layer_inverted_; }
@@ -421,11 +419,6 @@ class COMPOSITOR_EXPORT Layer
   // while attached to the main layer before the main layer is deleted.
   Layer* layer_mask_back_link_;
 
-  // When the layer is zoomed, this is the offset to the upper left corner of
-  // the area in the layer that is zoomed.
-  float zoom_x_offset_;
-  float zoom_y_offset_;
-
   // The zoom factor to scale the layer by.  Zooming is disabled when this is
   // set to 1.
   float zoom_;