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

ash/wm/overview/window_overview.cc

Index: ash/wm/overview/window_overview.cc
diff --git a/ash/wm/overview/window_overview.cc b/ash/wm/overview/window_overview.cc
index b37ea1639252cb2dc9f3c67d05b9f1827944d4f1..e7d914b6b3feb7eaf91b2dec884fc0513628dfba 100644
--- a/ash/wm/overview/window_overview.cc
+++ b/ash/wm/overview/window_overview.cc
@@ -314,8 +314,8 @@ aura::Window* WindowOverview::GetTargetedWindow(aura::Window* window) {
 }
 
 void WindowOverview::HideAndTrackNonOverviewWindows() {
-  Shell::RootWindowList root_windows = Shell::GetAllRootWindows();
-  for (Shell::RootWindowList::const_iterator root_iter = root_windows.begin();
+  aura::Window::Windows root_windows = Shell::GetAllRootWindows();
+  for (aura::Window::Windows::const_iterator root_iter = root_windows.begin();
        root_iter != root_windows.end(); ++root_iter) {
     for (size_t i = 0; i < kSwitchableWindowContainerIdsLength; ++i) {
       aura::Window* container = Shell::GetContainer(*root_iter,
@@ -349,7 +349,7 @@ void WindowOverview::PositionWindows() {
     }
     PositionWindowsOnRoot(single_root_window_, windows);
   } else {
-    Shell::RootWindowList root_window_list = Shell::GetAllRootWindows();
+    aura::Window::Windows root_window_list = Shell::GetAllRootWindows();
     for (size_t i = 0; i < root_window_list.size(); ++i)
       PositionWindowsFromRoot(root_window_list[i]);
   }