Adds a check to ensure that a NULL pointer from RenderViewHostImpl::FromID() is not dereferenced

content/browser/renderer_host/render_view_host_impl.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 "content/browser/renderer_host/render_view_host_impl.h"
 
 #include <set>
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 1020 matching lines @@
 
 void RenderViewHostImpl::OnMsgRunModal(int opener_id, IPC::Message* reply_msg) {
   DCHECK(!run_modal_reply_msg_);
   run_modal_reply_msg_ = reply_msg;
   run_modal_opener_id_ = opener_id;
 
   content::RecordAction(UserMetricsAction("ShowModalDialog"));
 
   RenderViewHostImpl* opener =
       RenderViewHostImpl::FromID(GetProcess()->GetID(), run_modal_opener_id_);
-  opener->StopHangMonitorTimeout();
-  // The ack for the mouse down won't come until the dialog closes, so fake it
-  // so that we don't get a timeout.
-  opener->decrement_in_flight_event_count();
+  if (opener) {
+    opener->StopHangMonitorTimeout();
+    // The ack for the mouse down won't come until the dialog closes, so fake it
+    // so that we don't get a timeout.
+    opener->decrement_in_flight_event_count();
+  }
 
   // TODO(darin): Bug 1107929: Need to inform our delegate to show this view in
   // an app-modal fashion.
 }
 
 void RenderViewHostImpl::OnMsgRenderViewReady() {
   render_view_termination_status_ = base::TERMINATION_STATUS_STILL_RUNNING;
   WasResized();
   delegate_->RenderViewReady(this);
 }
@@ skipping 828 matching lines @@
   // can cause navigations to be ignored in OnMsgNavigate.
   is_waiting_for_beforeunload_ack_ = false;
   is_waiting_for_unload_ack_ = false;
 }
 
 void RenderViewHostImpl::ClearPowerSaveBlockers() {
   STLDeleteValues(&power_save_blockers_);
 }
 
 }  // namespace content