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 1fa8244701377e3c0ff43412473b5a2ba9409c72..2827513821b209c568d9aa4fad38cf52ac53eaa5 100644
--- a/ash/magnifier/magnification_controller.cc
+++ b/ash/magnifier/magnification_controller.cc
@@ -46,6 +46,7 @@ class MagnificationControllerImpl : virtual public MagnificationController,
 
   // MagnificationController overrides:
   virtual void SetEnabled(bool enabled) OVERRIDE;
+  virtual bool IsEnabled() const 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;
@@ -426,6 +427,10 @@ void MagnificationControllerImpl::SetEnabled(bool enabled) {
   }
 }
 
+bool MagnificationControllerImpl::IsEnabled() const {
+  return is_enabled_;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // MagnificationControllerImpl: aura::EventFilter implementation