Move continue navigation callback to blink

This will make it easier to synchronously commit
navigations in blink until we are ready to stop using
WebURLLoader for main resources.

Bug: 855189
Change-Id: I097d65e83bf645b5ffd621fcf68d94d6280d15a1
Reviewed-on: https://chromium-review.googlesource.com/c/1359332
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616428}
8 files changed