Reland "Factor out reading and writing of preferences into |PrefStore|."

Reland "Factor out reading and writing of preferences into |PrefStore|."

The CL now applies after r45225 (Throw out preferences files that are corrupt rather than keeping them in read-only mode), which means that the changes in that commit moved to JsonPrefStore.

I updated JsonPrefStoreTest.InvalidFile to test the new behavior.

***

In order to implement platform-specific policies, reading and writing preferences needs to be abstracted from the |PrefService|. The interface for that is now |PrefStore|, with an implementation |JsonPrefStore|, which stores the pref data in a JSON file. There is another implementation, |DummyPrefStore|, which doesn't store any persistent preferences, and is currently used for tests.

Most of the changes are for using the new interface, which is |new PrefService(new JsonPrefStore(filename))| instead of |new PrefService(filename)|.

BUG=40259
TEST=PrefServiceTest.*:PrefServiceSetValueTest.*:PrefMemberTest.*:JsonPrefStoreTest.*

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=45309

[Bernhard Bauer, 2010-04-22 11:43:35]

Could you review this... again? :)

[Pam (message me for reviews), 2010-04-22 13:03:47]

LGTM. I only re-reviewed the three json_pref_store* files, and rubber-stamp the
rest on the assumption that they didn't change.

- Pam

http://codereview.chromium.org/1717007/diff/6001/1037
File chrome/browser/json_pref_store.cc (right):

http://codereview.chromium.org/1717007/diff/6001/1037#newcode78
chrome/browser/json_pref_store.cc:78: // TODO(erikkay) if we keep this error
checking for very long, we may want
Nit: 80 col