Using the Hydrogen code stub bailout mechanism is not correct for the
string length overflow check in the StringAddStub. Instead make sure we
just throw the proper exception.

R=mstarzinger@chromium.org
BUG=chromium:627934

Review-Url: https://codereview.chromium.org/2146353002
Cr-Commit-Position: refs/heads/master@{#37758}