Don't set error_detail to 'Unexpected State' just log it

BUG=299900
R=armansito@chromium.org, pneubeck@chromium.org

Review URL: https://codereview.chromium.org/24998008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226285 0039d316-1c4b-4281-b951-d872f2087c98
sync: Process updates responses on the sync thread

Convert ProcessUpdatesCommand from a ModelChangingSyncerCommand to a
SyncerCommand.  This means it will be executed only on the syncer
thread, rather than delegating to a collection of model threads.

In order to ensure this change is safe and will not be broken by future
CLs, it converts all transactions used by the ProcessUpdatesCommand into
ModelNeutralWriteTransactions.  When implemented correctly, this
guarantees that no change performed by this command will need to be
forwarded to the model threads.

This commit adds a constructor to ModelNeutralMutableEntry to allow it
to instantiate "update" items.  This is safe because these update items
can be saved and manipulated inside the sync directory as long as they
remain locally IS_DEL.  The native models do not need to be made aware
of them until this flag is unset when we apply the updates in a later
SyncerCommand.

BUG=299023

Review URL: https://codereview.chromium.org/24879002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226286 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226285
SVN changes up to revision 226286
Update iOS None-ing in DEPS

BUG=None

Review URL: https://codereview.chromium.org/25317002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226287 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226287