Use a weak pointer to determine if resizer was destroyed by nested Drag calls.

ash/wm/drag_window_resizer.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/drag_window_resizer.h"
 
 #include "ash/display/mouse_cursor_event_filter.h"
 #include "ash/screen_ash.h"
 #include "ash/shell.h"
 #include "ash/wm/coordinate_conversion.h"
 #include "ash/wm/drag_window_controller.h"
 #include "ash/wm/property_util.h"
+#include "base/memory/weak_ptr.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/env.h"
 #include "ui/aura/root_window.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_delegate.h"
 #include "ui/base/hit_test.h"
 #include "ui/base/ui_base_types.h"
 #include "ui/gfx/screen.h"
 
 namespace ash {
@@ skipping 26 matching lines @@
 // static
 DragWindowResizer* DragWindowResizer::instance_ = NULL;
 
 DragWindowResizer::~DragWindowResizer() {
   Shell* shell = Shell::GetInstance();
   shell->mouse_cursor_filter()->set_mouse_warp_mode(
       MouseCursorEventFilter::WARP_ALWAYS);
   shell->mouse_cursor_filter()->HideSharedEdgeIndicator();
   if (instance_ == this)
     instance_ = NULL;
-
-  if (destroyed_)
-    *destroyed_ = true;
 }
 
 // static
 DragWindowResizer* DragWindowResizer::Create(
     WindowResizer* next_window_resizer,
     aura::Window* window,
     const gfx::Point& location,
     int window_component,
     aura::client::WindowMoveSource source) {
   Details details(window, location, window_component, source);
   return details.is_resizable ?
       new DragWindowResizer(next_window_resizer, details) : NULL;
 }
 
 void DragWindowResizer::Drag(const gfx::Point& location, int event_flags) {
-  bool destroyed = false;
-  destroyed_ = &destroyed;
+  base::WeakPtr<DragWindowResizer> resizer(weak_ptr_factory_.GetWeakPtr());
   next_window_resizer_->Drag(location, event_flags);
+  if (!resizer)
+    return;
 
-  // TODO(flackr): Refactor the way WindowResizer calls into other window
-  // resizers to avoid the awkward pattern here for checking if
-  // next_window_resizer_ destroys the resizer object.
-  if (destroyed)
-    return;
-  destroyed_ = NULL;
   last_mouse_location_ = location;
-
   // Show a phantom window for dragging in another root window.
   if (HasSecondaryRootWindow()) {
     gfx::Point location_in_screen = location;
     wm::ConvertPointToScreen(GetTarget()->parent(), &location_in_screen);
     const bool in_original_root =
         wm::GetRootWindowAt(location_in_screen) == GetTarget()->GetRootWindow();
     UpdateDragWindow(GetTarget()->bounds(), in_original_root);
   } else {
     drag_window_controller_.reset();
   }
@@ skipping 34 matching lines @@
 }
 
 const gfx::Point& DragWindowResizer::GetInitialLocation() const {
   return details_.initial_location_in_parent;
 }
 
 DragWindowResizer::DragWindowResizer(WindowResizer* next_window_resizer,
                                      const Details& details)
     : next_window_resizer_(next_window_resizer),
       details_(details),
-      destroyed_(NULL) {
+      weak_ptr_factory_(this) {
   // The pointer should be confined in one display during resizing a window
   // because the window cannot span two displays at the same time anyway. The
   // exception is window/tab dragging operation. During that operation,
   // |mouse_warp_mode_| should be set to WARP_DRAG so that the user could move a
   // window/tab to another display.
   MouseCursorEventFilter* mouse_cursor_filter =
       Shell::GetInstance()->mouse_cursor_filter();
   mouse_cursor_filter->set_mouse_warp_mode(
       ShouldAllowMouseWarp() ?
       MouseCursorEventFilter::WARP_DRAG : MouseCursorEventFilter::WARP_NONE);
@@ skipping 47 matching lines @@
 
 bool DragWindowResizer::ShouldAllowMouseWarp() {
   return (details_.window_component == HTCAPTION) &&
       !GetTarget()->transient_parent() &&
       (GetTarget()->type() == aura::client::WINDOW_TYPE_NORMAL ||
        GetTarget()->type() == aura::client::WINDOW_TYPE_PANEL);
 }
 
 }  // namespace internal
 }  // namespace ash