GitLab

Many flaky sync tests cannot be reproduced locally and even flake
occasionally on bots. Hence, let's be verbose when they do fail, and
print a detailed trace of the sync traffic as experienced by the
FakeServer.

This is achieved by leveraging gTest's ScopedTrace.

Such detailed log should be, in many cases, sufficient to understand
what caused the flake.

Bug: 1017645,1014086
Change-Id: Icd9bf9637cfb6dd7da789aa0adee5c7161339b86
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1883651
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709907}