Fix crash in the HWNDMessageHandler::HandleMouseInputForCaption function.

ui/views/win/hwnd_message_handler.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 "ui/views/win/hwnd_message_handler.h"
 
 #include <dwmapi.h>
 #include <oleacc.h>
 #include <shellapi.h>
 #include <tchar.h>
@@ skipping 2539 matching lines @@
       }
       if (should_handle_pending_ncl_button_down) {
         l_param = MAKELPARAM(caption_left_button_click_pos_.x(),
                              caption_left_button_click_pos_.y());
         // TODO(msw): Eliminate undesired painting, or re-evaluate this
         // workaround.
         // DefWindowProc for WM_NCLBUTTONDOWN does weird non-client painting,
         // so we need to call it inside a ScopedRedrawLock. This may cause
         // other negative side-effects
         // (ex/ stifling non-client mouse releases).
+        // We may be deleted in the context of DefWindowProc. Don't refer to
+        // any member variables after the DefWindowProc call.
+        left_button_down_on_caption_ = false;
+
         if (delegate_->IsUsingCustomFrame()) {
           DefWindowProcWithRedrawLock(WM_NCLBUTTONDOWN, HTCAPTION, l_param);
         } else {
           DefWindowProc(hwnd(), WM_NCLBUTTONDOWN, HTCAPTION, l_param);
         }
-        left_button_down_on_caption_ = false;
       }
       break;
     }
 
     case WM_NCMOUSELEAVE:
       break;
 
     default:
       left_button_down_on_caption_ = false;
       break;
   }
   return handled;
 }
 
 
 }  // namespace views