Add the partial screen magnifier to Chrome OS.

ash/magnifier/magnification_controller.cc

Index: ash/magnifier/magnification_controller.cc
diff --git a/ash/magnifier/magnification_controller.cc b/ash/magnifier/magnification_controller.cc
index 091f6daf75ef9709470f75197269564f2e46c0b8..529241ab33e200192bc410e7c9b539a55153579a 100644
--- a/ash/magnifier/magnification_controller.cc
+++ b/ash/magnifier/magnification_controller.cc
@@ -45,6 +45,7 @@ class MagnificationControllerImpl : virtual public MagnificationController,
 
   // MagnificationController overrides:
   virtual void SetEnabled(bool enabled) OVERRIDE;
+  virtual bool IsEnabled() OVERRIDE;
   virtual void SetScale(float scale, bool animate) OVERRIDE;
   virtual float GetScale() const OVERRIDE { return scale_; }
   virtual void MoveWindow(int x, int y, bool animate) OVERRIDE;
@@ -413,6 +414,10 @@ void MagnificationControllerImpl::SetEnabled(bool enabled) {
   }
 }
 
+bool MagnificationControllerImpl::IsEnabled() {
+  return is_enabled_;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // MagnificationControllerImpl: aura::EventFilter implementation