Implement IOSChromeSyncClient::GetBookmarkUndoServiceIfExists().
Implement IOSChromeSyncClient::GetBookmarkUndoServiceIfExists().

BUG=561569

Review URL: https://codereview.chromium.org/1479223002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#361997}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk