Fixing flakiness of 2 AppActivityTest's

Fixing flakiness of 2 AppActivityTest's

This was caused by some very slow running trybots. If the test was running significantly slower
than a second, a MemoryPressureNotifier event was able to be sent, which caused the ResourceManager
to perform some asynchronous action which is not wanted for these unit tests.

BUG=412537, 417189
TEST=AppActivityTes.TestUnloadProxyLocation, AppActivityTest.TestMultipleActivityUnloadLock

Committed: https://crrev.com/d8cbcb4ebec718274aa5807ccfb785fb7cab275c
Cr-Commit-Position: refs/heads/master@{#296545}

[Mr4D (OOO till 08-26), 2014-09-24 20:06:37]

skuhne@chromium.org changed reviewers:
+ oshima@chromium.org

[Mr4D (OOO till 08-26), 2014-09-24 20:06:48]

Please have a look!

[oshima, 2014-09-24 21:40:56]

lgtm

[Mr4D (OOO till 08-26), 2014-09-24 21:48:22]

The CQ bit was checked by skuhne@chromium.org

[commit-bot: I haz the power, 2014-09-24 21:48:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/598033004/1

[commit-bot: I haz the power, 2014-09-24 22:28:24]

Committed patchset #1 (id:1) as bacfd1327b0ed9fca39d5c3e4d06e819a5444f05

[commit-bot: I haz the power, 2014-09-24 22:28:55]

Patchset 1 (id:??) landed as
https://crrev.com/d8cbcb4ebec718274aa5807ccfb785fb7cab275c
Cr-Commit-Position: refs/heads/master@{#296545}