Do not attempt to apply app sync updates to extensions with matching ID, or vice versa.

Do not attempt to apply app sync updates to extensions with matching ID, or vice versa.

BUG=chromium-os:19516
TEST=New unit test; also manually add a syncable app to profile, sync, then install extension with same ID: with change, no crash, without, crash on sync.
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=98662

[Ben Olmstead, 2011-08-26 17:59:37]

This fixes a crash on sync when sync has data for an app with the same ID as an
installed extension.  I believe this does not crash with the sync refactoring I
did, but a related problem will occur, so I will need to make an analogous fix
on trunk.

I also have not been able to verify that this is actually the problem originally
reported, but it does fix a Chrome startup crash.

[asargent_no_longer_on_chrome, 2011-08-26 18:30:19]

LGTM