GitLab

This CL adds an enum, SiteInstanceProcessAssignment, which
describes all the ways a SiteInstance may be assigned a render
process. This is exposed in the content API to allow embedders to
record this usage.

See design doc in bug and/or chained CL for more info.

Bug: 1129505
Change-Id: I0654d52b4c0fef3830a877fb1c1476dea4ad9361
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2417100
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809620}