DevTools: fix crash caused by dereferening empty handle

webkit/glue/devtools/debugger_agent_impl.cc

Index: webkit/glue/devtools/debugger_agent_impl.cc
diff --git a/webkit/glue/devtools/debugger_agent_impl.cc b/webkit/glue/devtools/debugger_agent_impl.cc
index 6a0d848f236d6ceeb0303017e30bf5caa97b0b8f..de80bad369abc0535261d2775e43d572e887b086 100644
--- a/webkit/glue/devtools/debugger_agent_impl.cc
+++ b/webkit/glue/devtools/debugger_agent_impl.cc
@@ -164,7 +164,11 @@ String DebuggerAgentImpl::ExecuteUtilityFunction(
   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);