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

ash/wm/toplevel_window_event_handler.cc

Index: ash/wm/toplevel_window_event_handler.cc
diff --git a/ash/wm/toplevel_window_event_handler.cc b/ash/wm/toplevel_window_event_handler.cc
index 4f0826986bba4e2188281a0a6d36e0e844fbf746..1cda284dcf74b71e658281d35fb8a45bbf8f5e20 100644
--- a/ash/wm/toplevel_window_event_handler.cc
+++ b/ash/wm/toplevel_window_event_handler.cc
@@ -59,6 +59,8 @@ class ToplevelWindowEventHandler::ScopedWindowResizer
                       WindowResizer* resizer);
   virtual ~ScopedWindowResizer();
 
+  WindowResizer* ReleaseResizer();
+
   WindowResizer* resizer() { return resizer_.get(); }
 
   // WindowObserver overrides:
@@ -88,6 +90,13 @@ ToplevelWindowEventHandler::ScopedWindowResizer::~ScopedWindowResizer() {
     resizer_->GetTarget()->RemoveObserver(this);
 }
 
+WindowResizer*
+ToplevelWindowEventHandler::ScopedWindowResizer::ReleaseResizer() {
+  if (resizer_.get())
+    resizer_->GetTarget()->RemoveObserver(this);
+  return resizer_.release();
+}
+
 void ToplevelWindowEventHandler::ScopedWindowResizer::OnWindowPropertyChanged(
     aura::Window* window,
     const void* key,
@@ -323,13 +332,27 @@ void ToplevelWindowEventHandler::OnDisplayConfigurationChanging() {
   }
 }
 
+void ToplevelWindowEventHandler::PassResizer(WindowResizerOwner* new_owner) {
+  DCHECK(window_resizer_.get());
+  new_owner->AcceptResizer(window_resizer_->ReleaseResizer(),
+                           in_gesture_drag_);
+  window_resizer_.reset();
+}
+
+void ToplevelWindowEventHandler::AcceptResizer(WindowResizer* resizer,
+                                               bool in_gesture_drag) {
+  window_resizer_.reset(new ScopedWindowResizer(this, resizer));
+  in_gesture_drag_ = in_gesture_drag;
+}
+
 void ToplevelWindowEventHandler::CreateScopedWindowResizer(
     aura::Window* window,
     const gfx::Point& point_in_parent,
     int window_component) {
   window_resizer_.reset();
   WindowResizer* resizer =
-      CreateWindowResizer(window, point_in_parent, window_component).release();
+      CreateWindowResizer(this, window, point_in_parent,
+                          window_component).release();
   if (resizer)
     window_resizer_.reset(new ScopedWindowResizer(this, resizer));
 }