Add debugging info to hopefully catch what's causing 6316

chrome/views/hwnd_view.cc

 // Copyright (c) 2006-2008 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/views/hwnd_view.h"
 
 #include "chrome/common/gfx/chrome_canvas.h"
 #include "chrome/common/win_util.h"
 #include "chrome/views/focus_manager.h"
 #include "chrome/views/scroll_view.h"
@@ skipping 13 matching lines @@
   // know when the position of any ancestor changes, or our visibility relative
   // to other views changed as it'll effect our position relative to the root.
   SetNotifyWhenVisibleBoundsInRootChanges(true);
 }
 
 HWNDView::~HWNDView() {
 }
 
 void HWNDView::Attach(HWND hwnd) {
   DCHECK(hwnd_ == NULL);
+  DCHECK(hwnd) << "Impossible detatched tab case; See crbug.com/6316";
+
   hwnd_ = hwnd;
 
   // First hide the new window. We don't want anything to draw (like sub-hwnd
   // borders), when we change the parent below.
   ShowWindow(hwnd_, SW_HIDE);
 
   // Need to set the HWND's parent before changing its size to avoid flashing.
   ::SetParent(hwnd_, GetWidget()->GetHWND());
   UpdateHWNDBounds();
 
@@ skipping 140 matching lines @@
   if (installed_clip_)
     canvas->FillRectInt(SkColorSetRGB(255, 255, 255), 0, 0, width(), height());
 }
 
 std::string HWNDView::GetClassName() const {
   return kViewClassName;
 }
 
 }  // namespace views