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

ash/shell/window_watcher.cc

Index: ash/shell/window_watcher.cc
diff --git a/ash/shell/window_watcher.cc b/ash/shell/window_watcher.cc
index 302a52328ab349443991dad006ae3efc551cb235..ea60dbcb868ddff9ebc949310aa9584180b67e5e 100644
--- a/ash/shell/window_watcher.cc
+++ b/ash/shell/window_watcher.cc
@@ -70,18 +70,18 @@ class WindowWatcher::WorkspaceWindowWatcher : public aura::WindowObserver {
 
 WindowWatcher::WindowWatcher() {
   workspace_window_watcher_.reset(new WorkspaceWindowWatcher(this));
-  Shell::RootWindowList root_windows = Shell::GetAllRootWindows();
-  for (Shell::RootWindowList::iterator iter = root_windows.begin();
+  aura::Window::Windows root_windows = Shell::GetAllRootWindows();
+  for (aura::Window::Windows::iterator iter = root_windows.begin();
        iter != root_windows.end(); ++ iter) {
     workspace_window_watcher_->RootWindowAdded(*iter);
   }
 }
 
 WindowWatcher::~WindowWatcher() {
-  Shell::RootWindowList root_windows = Shell::GetAllRootWindows();
-  for (Shell::RootWindowList::iterator iter = root_windows.begin();
+  aura::Window::Windows root_windows = Shell::GetAllRootWindows();
+  for (aura::Window::Windows::iterator iter = root_windows.begin();
        iter != root_windows.end(); ++ iter) {
-    workspace_window_watcher_->RootWindowRemoved(*iter);
+    workspace_window_watcher_->RootWindowRemoved((*iter)->GetDispatcher());
   }
 }