Check that an instance variable is non-NULL before use.

chrome/browser/ui/views/tabs/tab_drag_controller2.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 "chrome/browser/ui/views/tabs/tab_drag_controller2.h"
 
 #include <math.h>
 #include <set>
 
 #include "base/callback.h"
@@ skipping 963 matching lines @@
 
   browser->window()->Show();
   browser->window()->Activate();
   dragged_browser_view->GetWidget()->SetVisibilityChangedAnimationsEnabled(
       true);
   RunMoveLoop();
 }
 
 void TabDragController2::RunMoveLoop() {
   move_loop_browser_view_ = GetAttachedBrowserView();
+  DCHECK(move_loop_browser_view_);
   move_loop_browser_view_->set_move_observer(this);
   is_dragging_window_ = true;
   bool destroyed = false;
   destroyed_ = &destroyed;
   // Running the move loop release mouse capture on windows, which triggers
   // destroying the drag loop. Release mouse capture ourself before this while
   // the Dragcontroller isn't owned by the TabStrip.
   attached_tabstrip_->ReleaseDragController();
   attached_tabstrip_->GetWidget()->ReleaseMouseCapture();
   attached_tabstrip_->OwnDragController(this);
@@ skipping 436 matching lines @@
   browser->window()->SetBounds(new_bounds);
   return browser;
 }
 
 void TabDragController2::SetTrackedByWorkspace(gfx::NativeWindow window,
                                                bool value) {
 #if defined(USE_ASH)
   ash::SetTrackedByWorkspace(window, value);
 #endif
 }