GitLab

- Bookmark codec now takes in a ctor argument persist_ids
- If it's true, it will serialize IDs of bookmarks when encoding, and
  deserialize already serialized IDs (if present) when decoding.
- During decoding, unique-ify the IDs if they are not unique.
- Add unit tests for all new code.


Coming up in a separate changelist:
- Move ID generation logic to bookmark model, and make it non-static.

Review URL: http://codereview.chromium.org/99217

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@15013 0039d316-1c4b-4281-b951-d872f2087c98