Implement workspace scrubbing

ash/wm/workspace/workspace.cc

Index: ash/wm/workspace/workspace.cc
diff --git a/ash/wm/workspace/workspace.cc b/ash/wm/workspace/workspace.cc
index a2c03254b97e8606c15f5c9807a6ffd5e09057d9..a19d5329e891f90745af899cd0ac2a2f6842ef36 100644
--- a/ash/wm/workspace/workspace.cc
+++ b/ash/wm/workspace/workspace.cc
@@ -58,7 +58,22 @@ aura::Window* Workspace::ReleaseWindow() {
   return window;
 }
 
-bool Workspace::ShouldMoveToPending() const {
+aura::Window* Workspace::GetActiveWindow() const {
+  aura::Window* active_window = wm::GetActiveWindow();
+  if (!active_window)
+    return NULL;
+
+  // Only return the active window if it is in this workspace.
+  aura::Window* window = active_window;
+  while (window) {
+    if (window == window_)
+      return active_window;
+    window = window->parent();
+  }
+  return NULL;
+}
+
+bool Workspace::ShouldMoveToHidden() const {
   if (!is_maximized_)
     return false;