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* Add methods InitFromDB and SaveToDB to GDataDirectoryService, along with other helper methods to save/load the directory service from level db instead of from a proto file.
* Add a wrapper class GDataDirectoryServiceDB to hold the level db, with methods Create, Save, Read, Truncate, etc. This object lives on the blocking thread.
* Add CreateDBParams to facilitate creation of GDataDirectoryServiceDB on the blocking thread.
* Add GDataDirectoryService::FromProtoString to create a GDataEntry from a string saved in the db.
* Add unit tests for the db methods.
* Move LoadRootFeedParams to gdata_params. Move typedefs before struct definitions.
* Add a timer to measure the time to restore the filesystem from db or proto. For hugefileman, it's 3000 msec for db, and 2500 for proto, with debug code on a z600. Measurements on device TBD.

BUG=127856
TEST=unit tests, manual tests with hugefileman.
TBR=sky@chromium.org

Review URL: https://chromiumcodereview.appspot.com/10800092
Patch from Achuith Bhandarkar <achuith@chromium.org>.

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@150022 0039d316-1c4b-4281-b951-d872f2087c98