Reland Migrate SyncStoppedReporter to SimpleURLLoader

Original CL <https://chromium-review.googlesource.com/c/chromium/src/+/1089132>
was speculatively reverted after an unrelated CL was reverted which caused the
original CL to fail due to BUILD.gn changes.

This reland CL is identical to the original CL + BUILD.gn changes (and 1 include).

Patchset 1 is the original CL.
Patchset 3 is the reland.

Bug: 844966
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I20b832f3ba86278b2df423295ef2d62b6f7b65d6
TBR: [email protected], [email protected]
Reviewed-on: https://chromium-review.googlesource.com/1095325
Reviewed-by: Matt Menke <[email protected]>
Commit-Queue: Mark Pilgrim <[email protected]>
Cr-Commit-Position: refs/heads/master@{#566176}
16 files changed