DevTools: fix crash caused by dereferening empty handle

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 146 matching lines @@
 
   v8::Handle<v8::Value> args[] = {
     function_name_wrapper,
     json_args_wrapper,
     call_id_wrapper
   };
 
   v8::TryCatch try_catch;
   v8::Handle<v8::Value> res_obj = function->Call(context->Global(), 3, args);
   if (try_catch.HasCaught()) {
-    *exception = WebCore::toWebCoreString(try_catch.Message()->Get());
+    v8::Local<v8::Message> message = try_catch.Message();
+    if (message.IsEmpty())
+      *exception = "Unknown exception";
+    else
+      *exception = WebCore::toWebCoreString(message->Get());
     return "";
   } else {
     return WebCore::toWebCoreStringWithNullCheck(res_obj);
   }
 }
 
 void DebuggerAgentImpl::ExecuteVoidJavaScript(v8::Handle<v8::Context> context) {
   v8::HandleScope scope;
   ASSERT(!context.IsEmpty());
   v8::Context::Scope context_scope(context);
   DebuggerAgentManager::UtilityContextScope utility_scope;
 
   v8::Handle<v8::Value> function =
       context->Global()->Get(v8::String::New("devtools$$void"));
   ASSERT(function->IsFunction());
   v8::Handle<v8::Value> args[] = {
     v8::Local<v8::Value>()
   };
   v8::Handle<v8::Function>::Cast(function)->Call(context->Global(), 0, args);
 }
 
 WebCore::Page* DebuggerAgentImpl::GetPage() {
   return web_view_impl_->page();
 }