Cleanup ExtensionSyncService and SyncBundle.
- Merge AppSyncData into ExtensionSyncData.
- Remove duplication between AppSyncBundle and ExtensionSyncBundle by moving everything into the common SyncBundle.
- In SyncBundle, use consistent "push"/"apply" notation for changes going to/coming from Sync, rather than "process" for everything.
- Reduce the back-and-forth of ExtensionSyncService and SyncBundle calling into each other.
TBRing a straightforward change in two_client_apps_sync_test.cc
TBR=zea@chromium.org
BUG=None
Review URL: https://codereview.chromium.org/
1214923004
Cr-Commit-Position: refs/heads/master@{#337793}