Add persisted preference for projection touch HUD

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index 62ef0ff63a88ca6336dfe7b9ac944f7098f817f5..93192e8d7ba60df17bc43e69bc6bb253de95ab9c 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -462,11 +462,9 @@ class ASH_EXPORT Shell
   // Returns the launcher delegate, creating if necesary.
   LauncherDelegate* GetLauncherDelegate();
 
-  void SetTouchHudProjectionEnabled(bool enabled);
-
-  bool is_touch_hud_projection_enabled() const {
-    return is_touch_hud_projection_enabled_;
-  }
+  // Called when the preference for projection touch HUD is changed. It will
+  // show or hide the HUD based on the new preference value.
+  void TouchHudProjectionEnabledChanged(bool enabled);
 
  private:
   FRIEND_TEST_ALL_PREFIXES(ExtendedDesktopTest, TestCursor);
@@ -610,8 +608,6 @@ class ASH_EXPORT Shell
   // For testing only: simulate that a modal window is open
   bool simulate_modal_window_open_for_testing_;
 
-  bool is_touch_hud_projection_enabled_;
-
   DISALLOW_COPY_AND_ASSIGN(Shell);
 };