Fixed ExtensionUpdaterTest.TestMultipleManifestDownloading.

Fixed ExtensionUpdaterTest.TestMultipleManifestDownloading.

This test assumed that the ExtensionDownloader schedules its fetchers
in the order that StartUpdateCheck() is called, when downloading more
than one ManifestFetchData. However, the ExtensionDownloader was updated
in http://crrev.com/171540 to use a RequestQueue, which schedules the
fetchers using a heap.

That heap sorts the requests by time to the next retry, which is 0
for all requests initially. The test didn't break before because
std::push_heap and std::pop_heap in all STL implementations used
happen to keep the same order when all requests have the same
priority (!). This assumption broke under TSAN/MSAN builds because
they use libc++, whose std::pop_heap changes the order of the
execution of the fetches.

This fix makes the test support its fetches in any order.

BUG=358712
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=269554

[Joao da Silva, 2014-05-08 11:31:20]

PTAL, thanks!

[Marijn Kruisselbrink, 2014-05-08 20:41:48]

LGTM, thanks for fixing this

[Joao da Silva, 2014-05-09 07:24:59]

The CQ bit was checked by joaodasilva@chromium.org

[commit-bot: I haz the power, 2014-05-09 07:31:15]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/joaodasilva@chromium.org/271873002/20001

[commit-bot: I haz the power, 2014-05-10 07:50:11]

Change committed as 269554