Attach panel while dragging to bring it in front of other panels.

ash/wm/workspace/workspace_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/wm/workspace/workspace_manager.h"
 
 #include <algorithm>
 #include <functional>
 
 #include "ash/root_window_controller.h"
@@ skipping 230 matching lines @@
     // Clicking on the maximized window in a maximized workspace. Force all
     // other windows to drop to the desktop.
     MoveChildrenToDesktop(workspace->window(), NULL);
   }
 }
 
 Window* WorkspaceManager::GetActiveWorkspaceWindow() {
   return active_workspace_->window();
 }
 
+WorkspaceEventHandler* WorkspaceManager::GetEventHandlerForWindow(
+    aura::Window* window) {
+  return FindBy(window)->event_handler();
+}
+
 Window* WorkspaceManager::GetParentForNewWindow(Window* window) {
   // Try to put windows with transient parents in the same workspace as their
   // transient parent.
   if (window->transient_parent() && !IsMaximized(window)) {
     Workspace* workspace = FindBy(window->transient_parent());
     if (workspace)
       return workspace->window();
     // Fall through to normal logic.
   }
 
@@ skipping 538 matching lines @@
     new_workspace->window()->Show();
   ReparentWindow(window, new_workspace->window(), NULL);
   if (is_active) {
     SetActiveWorkspace(new_workspace, SWITCH_TRACKED_BY_WORKSPACE_CHANGED,
                        base::TimeDelta());
   }
 }
 
 }  // namespace internal
 }  // namespace ash