GitLab

|GetForWebContents| should only retrieve RuntimeManager for given web contents
and |GetOrCreateForWebContents| should create instance if one does not exist.

Bug: 1133783
Change-Id: Ib26162b69d1b3359fc571e139ba3724ec951aa12
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2453389Reviewed-by: Clemens Arbesser <arbesser@google.com>
Commit-Queue: Milica Selakovic <selakovic@google.com>
Cr-Commit-Position: refs/heads/master@{#814601}