Revert 228857 "Refactor HistoryDataStore into DictionaryDataStor..."

> Refactor HistoryDataStore into DictionaryDataStore+HistoryDataStore.
> Separate out the part that writes the dictionary to a file store into a separate class, DictionaryDataStore.
> 
> R=xiyuan@chromium.org
> BUG=None.
> TEST=Unit tests pass, search cross-session functionality works correctly.
> 
> Review URL: https://codereview.chromium.org/26179007

TBR=rkc@chromium.org

Review URL: https://codereview.chromium.org/27031006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228962 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228962