DecidePolicyForNavigation should only be called for content-initiated

Adding CHECKs to verify that we did not miss any cases when it's called
for browser-initiated navigation. Will cleanup after a couple of Canaries.

Bug: 789577

Change-Id: I36890e1cb653a7f1795a187be0d80f2a99e10aaf
Reviewed-on: https://chromium-review.googlesource.com/1135934
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Camille Lamy <clamy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575371}
1 file changed