Replace drainUntilIdle with a dispatch_barrier_sync for Breakpad tests

Replace drainUntilIdle with a dispatch_barrier_sync for Breakpad tests

drainUntilIdle was a crutch because it didn't fully eliminate the race
condition between Breakpad setting its state on its own queue and the
tests.
This CL adds a test method to get the BreakpadController queue and
dispatches a barrier block on it to wait until the BreakpadController
updated its state.

Previously:
https://codereview.chromium.org/2760973002/
https://codereview.chromium.org/2775403003/

BUG=700839
R=baxley@chromium.org
CC=olivierrobin@chromium.or

Review-Url: https://codereview.chromium.org/2827313002
Cr-Commit-Position: refs/heads/master@{#466065}
(cherry picked from commit 5895ccc48d4395a1b5359a6ca8ca9eb654d4cd3d)

Review-Url: https://codereview.chromium.org/2837483003 .
Cr-Commit-Position: refs/branch-heads/3071@{#119}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed: https://chromium.googlesource.com/chromium/src/+/20d59625dac84ed76c03f45b49a1f3979e5f9be1

[lpromero, 2017-04-21 10:31:28]

Description was changed from

==========
Replace drainUntilIdle with a dispatch_barrier_sync for Breakpad tests

drainUntilIdle was a crutch because it didn't fully eliminate the race
condition between Breakpad setting its state on its own queue and the
tests.
This CL adds a test method to get the BreakpadController queue and
dispatches a barrier block on it to wait until the BreakpadController
updated its state.

Previously:
https://codereview.chromium.org/2760973002/
https://codereview.chromium.org/2775403003/

BUG=700839
R=baxley@chromium.org
CC=olivierrobin@chromium.or

Review-Url: https://codereview.chromium.org/2827313002
Cr-Commit-Position: refs/heads/master@{#466065}
(cherry picked from commit 5895ccc48d4395a1b5359a6ca8ca9eb654d4cd3d)
==========

to

==========
Replace drainUntilIdle with a dispatch_barrier_sync for Breakpad tests

drainUntilIdle was a crutch because it didn't fully eliminate the race
condition between Breakpad setting its state on its own queue and the
tests.
This CL adds a test method to get the BreakpadController queue and
dispatches a barrier block on it to wait until the BreakpadController
updated its state.

Previously:
https://codereview.chromium.org/2760973002/
https://codereview.chromium.org/2775403003/

BUG=700839
R=baxley@chromium.org
CC=olivierrobin@chromium.or

Review-Url: https://codereview.chromium.org/2827313002
Cr-Commit-Position: refs/heads/master@{#466065}
(cherry picked from commit 5895ccc48d4395a1b5359a6ca8ca9eb654d4cd3d)

Review-Url: https://codereview.chromium.org/2837483003 .
Cr-Commit-Position: refs/branch-heads/3071@{#119}
Cr-Branched-From:
a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed:
https://chromium.googlesource.com/chromium/src/+/20d59625dac84ed76c03f45b49a1...
==========

[lpromero, 2017-04-21 10:31:29]

Committed patchset #1 (id:1) manually as
20d59625dac84ed76c03f45b49a1f3979e5f9be1.