GitLab

 - Fix beacon-common.sub.js and so that it can handle exceptions thrown
   from sendBeacon.
 - Simplify beacon-common.sub.js.
 - Remove navigate.iFrame.sub.html. Replace it with scripts in the
   main page.

Bug: 876670, 626703, 848275, 876669
Change-Id: I847dec3a71b27c76df156326637be243876daaab
Reviewed-on: https://chromium-review.googlesource.com/1237796Reviewed-by: Adam Rice <ricea@chromium.org>
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595780}