Password sync refactoring: implemented ProcessSyncChanges() and GetAllSyncData()

BUG=95758

Review URL: https://codereview.chromium.org/139443004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250944 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250944