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 f0ab7322a5e920678eda5b56d2a1b2051b2bfff8..fc9a0c9be4c7970fa72b3afc307db5f2dc8455c0 100644
--- a/ash/magnifier/magnification_controller.cc
+++ b/ash/magnifier/magnification_controller.cc
@@ -47,6 +47,7 @@ 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;
@@ -433,6 +434,10 @@ void MagnificationControllerImpl::SetEnabled(bool enabled) {
   }
 }
 
+bool MagnificationControllerImpl::IsEnabled() const {
+  return is_enabled_;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // MagnificationControllerImpl: aura::EventFilter implementation