DevTools: Fix access violation (null pointer) on document tear down.

webkit/glue/devtools/debugger_agent_impl.cc

 // Copyright (c) 2009 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 "config.h"
 
 #include <wtf/HashSet.h>
 #include <wtf/RefPtr.h>
 #include <wtf/Vector.h>
 
@@ skipping 43 matching lines @@
 
 void DebuggerAgentImpl::DebugBreak() {
   DebuggerAgentManager::DebugBreak(this);
 }
 
 void DebuggerAgentImpl::DebuggerOutput(const std::string& command) {
   delegate_->DebuggerOutput(command);
   webdevtools_agent_->ForceRepaint();
 }
 
-void DebuggerAgentImpl::CreateUtilityContext(
+void DebuggerAgentImpl::ResetUtilityContext(
     Document* document,
     v8::Persistent<v8::Context>* context) {
   if (!context->IsEmpty()) {
     context->Dispose();
   }
+  if (!document) {
+    return;
+  }
   v8::HandleScope scope;
 
   // TODO(pfeldman): Validate against Soeren.
   // Set up the DOM window as the prototype of the new global object.
   v8::Handle<v8::Context> window_context =
       V8Proxy::GetContext(document->frame());
   v8::Handle<v8::Object> window_global = window_context->Global();
   v8::Handle<v8::Value> window_wrapper =
       V8Proxy::LookupDOMWrapper(V8ClassIndex::DOMWINDOW, window_global);
 
@@ skipping 92 matching lines @@
   for (HashSet<DebuggerAgentImpl*>::const_iterator ag_it = agents.begin();
        ag_it != agents.end(); ++ag_it) {
     (*ag_it)->web_view()->SetIgnoreInputEvents(false);
   }
   deleteAllValues(deferrers);
 }
 
 WebCore::Page* DebuggerAgentImpl::GetPage() {
   return web_view_impl_->page();
 }