Fixing issues with new activity image readback

Fixing issues with new activity image readback

While writing the unit tests I have found problems and fixed them. Since I am not sure when the unit tests will land however (they come with the new Athena Browser test framework) I created this patch to get a workable version for Sadrul's Overview mode work.

BUG=408837
TEST=tests are in different CL which introduces Browser Tests for Athena

Committed: https://crrev.com/b5524e546f366cb73f7f50651919623bb5f0913e
Cr-Commit-Position: refs/heads/master@{#297193}

[Mr4D (OOO till 08-26), 2014-09-27 16:29:21]

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

[Mr4D (OOO till 08-26), 2014-09-27 16:29:22]

Please have a look! I hope this helps with your overview mode changes.

Please note that as long as we are not saving the PNG files to disc, you will
still see images being empty after a system start.

[sadrul, 2014-09-29 15:55:12]

lgtm

[Mr4D (OOO till 08-26), 2014-09-29 16:12:10]

The CQ bit was checked by skuhne@chromium.org

[commit-bot: I haz the power, 2014-09-29 16:12:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/611773002/1

[commit-bot: I haz the power, 2014-09-29 16:51:58]

Committed patchset #1 (id:1) as 73c1ee8c9eb4a35bd6fad0884f4dabc7b36f0ba7

[commit-bot: I haz the power, 2014-09-29 16:52:53]

Patchset 1 (id:??) landed as
https://crrev.com/b5524e546f366cb73f7f50651919623bb5f0913e
Cr-Commit-Position: refs/heads/master@{#297193}