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

ash/drag_drop/drag_drop_controller_unittest.cc

Index: ash/drag_drop/drag_drop_controller_unittest.cc
diff --git a/ash/drag_drop/drag_drop_controller_unittest.cc b/ash/drag_drop/drag_drop_controller_unittest.cc
index fa4f2bcde2afe4a4c8b50002caebdb136ecf9736..6e13a444688b04a57e9f9b94d4ef1e75f5945818 100644
--- a/ash/drag_drop/drag_drop_controller_unittest.cc
+++ b/ash/drag_drop/drag_drop_controller_unittest.cc
@@ -1020,9 +1020,9 @@ TEST_F(DragDropControllerTest, DragCancelAcrossDisplays) {
     return;
 
   UpdateDisplay("400x400,400x400");
-  Shell::RootWindowList root_windows =
+  aura::Window::Windows root_windows =
       Shell::GetInstance()->GetAllRootWindows();
-  for (Shell::RootWindowList::iterator iter = root_windows.begin();
+  for (aura::Window::Windows::iterator iter = root_windows.begin();
        iter != root_windows.end(); ++iter) {
     aura::client::SetDragDropClient(*iter, drag_drop_controller_.get());
   }
@@ -1099,7 +1099,7 @@ TEST_F(DragDropControllerTest, DragCancelAcrossDisplays) {
 
     EXPECT_EQ("405,405", observer.window_location_on_destroying().ToString());
   }
-  for (Shell::RootWindowList::iterator iter = root_windows.begin();
+  for (aura::Window::Windows::iterator iter = root_windows.begin();
        iter != root_windows.end(); ++iter) {
     aura::client::SetDragDropClient(*iter, NULL);
   }