Add the partial screen magnifier to Chrome OS.

ui/compositor/layer.h

Index: ui/compositor/layer.h
diff --git a/ui/compositor/layer.h b/ui/compositor/layer.h
index fa2c474a11c0f42c42163a7e8ebeee5d6f87cac0..09289970cd5c8ec983b08c877fee0201e8e84d6b 100644
--- a/ui/compositor/layer.h
+++ b/ui/compositor/layer.h
@@ -168,6 +168,9 @@ class COMPOSITOR_EXPORT Layer
   // grayscale otherwise.
   float GetTargetGrayscale() const;
 
+  // Zoom the background by this amount.
+  void SetBackgroundZoom(float x_offset, float y_offset, float zoom);
+
   // Invert the layer.
   bool layer_inverted() const { return layer_inverted_; }
   void SetLayerInverted(bool inverted);
@@ -371,6 +374,10 @@ class COMPOSITOR_EXPORT Layer
   // while attached to the main layer before the main layer is deleted.
   Layer* layer_mask_back_link_;
 
+  float zoom_x_offset_;
+  float zoom_y_offset_;
+  float zoom_;
+
   std::string name_;
 
   LayerDelegate* delegate_;