Add UpdateSyncMetadata, ClearSyncMetadata, UpdateModelTypeState,
ClearModelTypeState into SyncMetadataStore interface.
Let AutofillTable inherit SyncMetadataStore.
Also create a SyncMetadataStoreChangeList for autofill.
Will do this change for typed url in next CL.

BUG=708275

Review-Url: https://codereview.chromium.org/2794413002
Cr-Commit-Position: refs/heads/master@{#466568}
9 files changed