Remove parent* arg from GDataEntry ctor.

* Remove static FromDocumentEntry from GDataEntry, GDataFile, GDataDirectory. Replace with InitFromDocumentEntry.
* Move common code from GDataFile::InitFromDocumentEntry and GDataDirectory::InitFromDocumentEntry to GDataEntry::InitFromDocumentEntry.
* Add GDataDirectoryService::FromDocumentEntry and use this everywhere.
* Make ctors of GDataFile, GDataDirectory private, so these must be created by GDataDirectoryService's CreateGDataFile and
CreateGDataDirectory. Make GDataEntry ctor protected.

BUG=141494
TEST=unit tests.
Review URL: https://chromiumcodereview.appspot.com/10854083

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@151008 0039d316-1c4b-4281-b951-d872f2087c98
GDataFileError GDataFileSystem::UpdateFromFeedForTesting(
    const std::vector<DocumentFeed*>& feed_list,
    int64 start_changestamp,
    int64 root_feed_changestamp) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));

  return feed_loader_->UpdateFromFeed(feed_list,
                                      start_changestamp,
                                      root_feed_changestamp);
}

GDataFileError GDataFileSystem::UpdateFromFeedForTesting(
    const std::vector<DocumentFeed*>& feed_list,
    int64 start_changestamp,
    int64 root_feed_changestamp) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));

  return feed_loader_->UpdateFromFeed(feed_list,
                                      start_changestamp,
                                      root_feed_changestamp);
}
