[Android] Replace a synchronous callsite of GetAccounts()

[Android] Replace a synchronous callsite of GetAccounts().

Two misc changes from http://crrev.com/1380103004
Use a static JNI call from java to C++.
Make the GetAccounts method asynchronous.

TBR=rogerta@chromium.org

BUG=517697
Committed: https://crrev.com/b518f755450b62b644a1a734dd405cb762dcb81d
Cr-Commit-Position: refs/heads/master@{#354517}

[knn, 2015-10-16 12:33:11]

knn@chromium.org changed reviewers:
+ nyquist@chromium.org, rogerta@chromium.org

[knn, 2015-10-16 12:33:11]

knn@chromium.org changed required reviewers:
+ nyquist@chromium.org

[knn, 2015-10-16 12:33:12]

Separating unrelated changes from
http://crrev.com/1380103004 to a different patch.

PTAL. Thanks!

[nyquist, 2015-10-16 14:00:30]

lgtm

[knn, 2015-10-16 14:06:03]

The CQ bit was checked by knn@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-10-16 14:06:10]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1405353002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1405353002/1

[commit-bot: I haz the power, 2015-10-16 15:30:58]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-10-16 15:30:58]

Dry run: This issue passed the CQ dry run.

[knn, 2015-10-16 15:40:22]

Roger, I am TBRing you for an unused header include removal.

[knn, 2015-10-16 15:40:30]

The CQ bit was checked by knn@chromium.org

[commit-bot: I haz the power, 2015-10-16 15:40:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1405353002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1405353002/1

[commit-bot: I haz the power, 2015-10-16 15:45:03]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-16 15:46:04]

Patchset 1 (id:??) landed as
https://crrev.com/b518f755450b62b644a1a734dd405cb762dcb81d
Cr-Commit-Position: refs/heads/master@{#354517}

[Roger Tawa OOO till Jul 10th, 2015-10-16 17:49:03]

https://codereview.chromium.org/1405353002/diff/1/chrome/browser/android/sign...
File chrome/browser/android/signin/account_tracker_service_android.cc (right):

https://codereview.chromium.org/1405353002/diff/1/chrome/browser/android/sign...
chrome/browser/android/signin/account_tracker_service_android.cc:34:
account_tracker_service_->SeedAccountInfo(gaia_ids[i], account_names[i]);
Remove trailing _