Fix crashers in GetPrimaryDisplay

ash/display/display_controller.h

Index: ash/display/display_controller.h
diff --git a/ash/display/display_controller.h b/ash/display/display_controller.h
index ac513cd846efd4dbb474215fc3bf183a6b0e1d1f..0c00cfb3b6463e03001c54cf709124a70393ea00 100644
--- a/ash/display/display_controller.h
+++ b/ash/display/display_controller.h
@@ -83,6 +83,10 @@ class ASH_EXPORT DisplayController : public aura::DisplayObserver {
   DisplayController();
   virtual ~DisplayController();
 
+  // Gets primary display. This information is stored in global
+  // object as this can be accessed after Shell is closed.
+  static const gfx::Display& GetPrimaryDisplay();

[Daniel Erat, 2012/09/19 20:47:33]

nit: returning a reference to an internal pointer feels a bit strange.  could
you make this return const gfx::Display* or just a gfx::Display (since it looks
like this gets copied downstream) instead?

[oshima, 2012/09/19 21:21:28]

This pattern isn't uncommon in chrome (quick search of "  const\s[^\s]*&.*(" in
header shows a lot, although it doesn't necessarily mean it's ok just because
it's common :) 
and this won't cause real issue as this is global object which should outlive
UI.
Or are you worrying about because it may be deleted DisplayController's
constructor?

I'm happy to make this change as gfx::Display is treated as POD, but want to
understand
your concern before making the change.

[Daniel Erat, 2012/09/19 21:31:47]

Accessors that return const references are super-common for members that are
embedded within the class (since you know that the reference will be valid for
the lifetime of the object), but seem very rare for pointer members -- I only
see six files when I grep for 'const\s[^\s]*&.*(.*return \*'.  It makes me
nervous since it's possible for the reference to become invalid while the object
is still alive, if the object's pointer gets updated to point somewhere else.

+
   // Initializes primary display.
   void InitPrimaryDisplay();
 
@@ -99,10 +103,8 @@ class ASH_EXPORT DisplayController : public aura::DisplayObserver {
   // Returns the root window for |display_id|.
   aura::RootWindow* GetRootWindowForDisplayId(int64 id);
 
-  // Sets/Gets primary display.
-  const gfx::Display& primary_display() const {
-    return primary_display_;
-  }
+  // Sets primary display. This re-assigns the current root
+  // window to given |display|.
   void SetPrimaryDisplay(const gfx::Display& display);
 
   // Returns the secondary display.
@@ -160,8 +162,6 @@ class ASH_EXPORT DisplayController : public aura::DisplayObserver {
 
   ObserverList<Observer> observers_;
 
-  gfx::Display primary_display_;
-
   DISALLOW_COPY_AND_ASSIGN(DisplayController);
 };