Split Screen mode implementation

ui/wm/core/window_list_provider.h

+#ifndef UI_WM_CORE_WINDOW_LIST_PROVIDER_H_
+#define UI_WM_CORE_WINDOW_LIST_PROVIDER_H_
+
+#include "ui/aura/window.h"
+
+namespace wm {
+
+// Interface for an ordered list of aura::Window objects.
+class WindowListProvider {

[oshima, 2014/08/06 21:54:10]

move this to athena/wm/public.

The plan is that we'll have a class that manges manages the list of activities
(which may not have an associated aura window). stefan will rename and move this
later, but a/wm/public is fine for now.

Please add GetInstance and keep it separated from WindowManagerImpl.

[sadrul, 2014/08/07 15:26:16]

ActivityManager would be a good place for this. Its responsibility is to keep
track of the activities, and should be able to give us the list in the right
order.

[mfomitchev, 2014/08/08 16:03:23]

I moved the file. Did not add GetInstance() and didn't separate from
WindowManagerImpl.. Currently MruWindowTracker's constructor needs Window
Manager's container so that it can listen to new windows being added, so it
makes sense to create it from Window Manager and for the window manager to own
it. Once we have this wired to activities, I guess the mechanism will change.
Can we wait with doing the rest of the changes until then?

[oshima, 2014/08/08 16:45:34]

They simply shares the same container, but no true ownership relation between
them.
But I'm ok as this will change anyway. 

[mfomitchev, 2014/08/08 17:40:50]

Ah, good point.

+ public:
+  virtual ~WindowListProvider() {}
+
+  // Returns an ordered list of windows.
+  virtual aura::Window::Windows GetWindowList() = 0;
+  // Moves the window to the front of the list.
+  virtual void MoveToFront(aura::Window* window) = 0;
+};
+
+}  // namespace wm
+
+#endif  // UI_WM_CORE_WINDOW_LIST_PROVIDER_H_