Fix crash in InspectorHeapProfilerAgent::getHeapObjectId

ScriptScope should be created before calling ScriptValue::isUndefined to make sure there is a v8::HandleScope which is expected by ScriptValue::isUndefined implementation.

BUG=None
R=loislo@chromium.org

Review URL: https://codereview.chromium.org/64023002

git-svn-id: svn://svn.chromium.org/blink/trunk@161517 bbb929c8-8fbe-4397-9dbb-9b2b20218538