Domain Reliability: Don't clear "upload pending" bit until upload starts

Domain Reliability: Don't clear "upload pending" bit until upload starts

Someone noticed that occasionally the uploader sent an empty upload. I
looked into the scheduler and found that it was clearing the "upload
pending" bit early, when the upload was scheduled. This meant that if a
beacon arrived between scheduling and starting the upload, the bit was
still set on its behalf, despite it being included in the upload. Once
the upload finished, the scheduler would see the bit still set and
schedule another.

This patch adds a couple of unittests for interesting interleavings
(beacons that arrive between scheduling and starting the upload, and
between starting and finishing the upload), and clears the upload
pending bit in the right place.

BUG=356791
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=269592

[Deprecated (see juliatuttle), 2014-05-09 00:07:19]

PTAL, davidben.

[davidben, 2014-05-09 15:39:02]

lgtm

[Deprecated (see juliatuttle), 2014-05-09 15:39:14]

The CQ bit was checked by ttuttle@chromium.org

[commit-bot: I haz the power, 2014-05-09 15:40:45]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ttuttle@chromium.org/272773004/1

[Deprecated (see juliatuttle), 2014-05-10 04:01:57]

The CQ bit was checked by ttuttle@chromium.org

[commit-bot: I haz the power, 2014-05-10 04:02:57]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ttuttle@chromium.org/272773004/20001

[commit-bot: I haz the power, 2014-05-10 07:35:39]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  mac_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/mac_chromium_rel/buil...)
  win_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_rel/buil...)

[commit-bot: I haz the power, 2014-05-10 18:23:11]

Change committed as 269592