[Merge To M54]arc: Fix race when arc package sync service starts.

[Merge To M54]arc: Fix race when arc package sync service starts.
Fix the race which happens between initial packagelist refreshed and sync
DataTypeController::OnModelStarted by changing the observer of
OnAppInstanceReady() to OnPackageListInitialRefreshed().

BUG=652470
TBR=xiyuan@chromium.org, pavely@chromium.org, khmel@chromium.org
Test=Manual Test. Sync service always starts after arc packagelist
refreshes correctly.
Test=Pass sync integration test.

Review-Url: https://codereview.chromium.org/2389763003
Cr-Commit-Position: refs/heads/master@{#423362}
(cherry picked from commit 88a14008509adefe2b764ccb573ba629ba68dac5)

Committed: https://chromium.googlesource.com/chromium/src/+/e24af55b17c3554262658d03395bc48ca05deb4a

[Josh Horwich, 2016-10-12 00:21:23]

Description was changed from

==========
[Merge To M54]arc: Fix race when arc package sync service starts.
Fix the race which happens between initial packagelist refreshed and sync
DataTypeController::OnModelStarted by changing the observer of
OnAppInstanceReady() to OnPackageListInitialRefreshed().

BUG=652470
TBR=xiyuan@chromium.org, pavely@chromium.org, khmel@chromium.org
Test=Manual Test. Sync service always starts after arc packagelist
refreshes correctly.
Test=Pass sync integration test.

Review-Url: https://codereview.chromium.org/2389763003
Cr-Commit-Position: refs/heads/master@{#423362}
(cherry picked from commit 88a14008509adefe2b764ccb573ba629ba68dac5)
==========

to

==========
[Merge To M54]arc: Fix race when arc package sync service starts.
Fix the race which happens between initial packagelist refreshed and sync
DataTypeController::OnModelStarted by changing the observer of
OnAppInstanceReady() to OnPackageListInitialRefreshed().

BUG=652470
TBR=xiyuan@chromium.org, pavely@chromium.org, khmel@chromium.org
Test=Manual Test. Sync service always starts after arc packagelist
refreshes correctly.
Test=Pass sync integration test.

Review-Url: https://codereview.chromium.org/2389763003
Cr-Commit-Position: refs/heads/master@{#423362}
(cherry picked from commit 88a14008509adefe2b764ccb573ba629ba68dac5)

Committed:
https://chromium.googlesource.com/chromium/src/+/e24af55b17c3554262658d03395b...
==========

[Josh Horwich, 2016-10-12 00:21:24]

Committed patchset #1 (id:1) manually as
e24af55b17c3554262658d03395bc48ca05deb4a (presubmit successful).