Add a note to URLFetcher that it shouldn't be use in content embedders.

Also add a presubmit warning to trigger on new/modified uses of
URLFetcher.

Bug: 746977, 598073
Change-Id: I962a9f9bdb0c8c533f5cc4e7ca5a919f917a89ca
Reviewed-on: https://chromium-review.googlesource.com/984512
Reviewed-by: Helen Li <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Commit-Queue: Matt Menke <[email protected]>
Cr-Commit-Position: refs/heads/master@{#546605}
2 files changed