Fix unresponsive browser due to a crashed/hung plugin with a modal dialog.

chrome/browser/hang_monitor/hung_window_detector.cc

 // Copyright (c) 2011 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/hang_monitor/hung_window_detector.h"
 
 #include <windows.h>
 #include <atlbase.h>
 
 #include "base/logging.h"
@@ skipping 41 matching lines @@
     // If we already are checking for hung windows on another thread,
     // don't do this again.
     if (enumerating_) {
       return;
     }
     enumerating_ = true;
   } while (false);  // To scope the AutoLock
 
   EnumChildWindows(top_level_window_, ChildWndEnumProc,
                    reinterpret_cast<LPARAM>(this));
+
+  // The window shouldn't be disabled unless we're showing a modal dialog.
+  // If we're not, then reenable the window.
+  if (!::IsWindowEnabled(top_level_window_) &&
+      !::GetWindow(top_level_window_, GW_ENABLEDPOPUP)) {
+    ::EnableWindow(top_level_window_, TRUE);
+  }
+
   enumerating_ = false;
 }
 
 bool HungWindowDetector::CheckChildWindow(HWND child_window) {
   // It can happen that the window is DOA. It specifically happens
   // when we have just killed a plugin process and the enum is still
   // enumerating windows from that process.
   if (!IsWindow(child_window))  {
     return true;
   }
@@ skipping 97 matching lines @@
                                                    LPARAM param) {
   HungWindowDetector* detector_instance =
       reinterpret_cast<HungWindowDetector*>(param);
   if (NULL == detector_instance) {
     NOTREACHED();
     return FALSE;
   }
 
   return detector_instance->CheckChildWindow(child_window);
 }