Eliminate Shell::RootWindowList in favor of aura::Window::Windows.

ash/wm/drag_window_resizer.cc

Index: ash/wm/drag_window_resizer.cc
diff --git a/ash/wm/drag_window_resizer.cc b/ash/wm/drag_window_resizer.cc
index 5713cf8392571e62b8f16dc34e92528c1368f4af..000d1198419d9d40656f89f97839ebf1bb8813e3 100644
--- a/ash/wm/drag_window_resizer.cc
+++ b/ash/wm/drag_window_resizer.cc
@@ -41,8 +41,8 @@ bool HasSecondaryRootWindow() {
 
 // When there are two root windows, returns one of the root windows which is not
 // |root_window|. Returns NULL if only one root window exists.
-aura::RootWindow* GetAnotherRootWindow(aura::Window* root_window) {
-  Shell::RootWindowList root_windows = Shell::GetAllRootWindows();
+aura::Window* GetAnotherRootWindow(aura::Window* root_window) {
+  aura::Window::Windows root_windows = Shell::GetAllRootWindows();
   if (root_windows.size() < 2)
     return NULL;
   DCHECK_EQ(2U, root_windows.size());