DevTools: Fix Crash Report - v8::Value::IsInt32.

BUG=397440
R=yurys

Review URL: https://codereview.chromium.org/416363002

git-svn-id: svn://svn.chromium.org/blink/trunk@179116 bbb929c8-8fbe-4397-9dbb-9b2b20218538