Revert 230025 "Extract the in-memory model from DomDistillerStore"

It caused "Use of uninitialised values" in the Linux valgrind bot:
http://build.chromium.org/p/chromium.memory.fyi/builders/Linux%20Tests%20%28valgrind%29%282%29/builds/31483

> Extract the in-memory model from DomDistillerStore
> 
> This moves interaction with the in-memory model from the store to its
> own class: DomDistillerModel. This also adds two ways to lookup entries
> to both the store and the model, GetEntryById and GetEntryByUrl.
> 
> BUG=288015
> TBR=joi@chromium.org
> 
> Review URL: https://codereview.chromium.org/26574002

TBR=cjhopman@chromium.org

Review URL: https://codereview.chromium.org/34363003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230057 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230057