Blink-in-JS: Allow a stackoverflow error thrown by private scripts

Currently standard JS errors thrown by private scripts are treated
as real errors of the private scripts and crash the renderer.
However, we need to special-case a stackoverflow error because
user's script can create code that causes a stackoverflow error
in private scripts.

BUG=412143
TEST=fast/dom/private_script_unittest.html

Review URL: https://codereview.chromium.org/553983007

git-svn-id: svn://svn.chromium.org/blink/trunk@181603 bbb929c8-8fbe-4397-9dbb-9b2b20218538