Ignore Javascript urls dropped on tabs (Mac version)

When a Javascript: url is dropped on a tab, it executes in the
security context of the selected tab, representing a script
injection attack ("Dropjacking"). We will match other browsers
and disallow such drops.

Mac handles URL drops using a different codepath than Windows;
this change fixes the Mac codepath.

BUG=639750

Review-Url: https://codereview.chromium.org/2346023002
Cr-Commit-Position: refs/heads/master@{#419266}
2 files changed