Relocate reuseable portions of ash/display/display_util.*

ash/display/display_manager.h

Index: ash/display/display_manager.h
diff --git a/ash/display/display_manager.h b/ash/display/display_manager.h
index ddbbea34b55c14764a592692e955f9b05a2096bc..9730b3a2117ad9d85a588aef6ccb37c64e563dc8 100644
--- a/ash/display/display_manager.h
+++ b/ash/display/display_manager.h
@@ -342,6 +342,12 @@ class ASH_EXPORT DisplayManager
   // for this test scenario.
   void UpdateInternalManagedDisplayModeListForTest();
 
+  // Zoom the internal display.
+  bool ZoomInternalDisplay(bool up);
+
+  // Reset the internal display zoom.
+  void ResetInternalDisplayZoom();
+
  private:
   FRIEND_TEST_ALL_PREFIXES(ExtendedDesktopTest, ConvertPoint);
   FRIEND_TEST_ALL_PREFIXES(DisplayManagerTest, TestNativeDisplaysChanged);