sync is actually part of Chromium[1][2]. The big parts are probably the PDF viewer, as you said, and Flash. Chromium also ships with fewer codecs than Chrome (e.g. no h264), but I'm not sure if they're from closed source or just not licensed for redistribution. There's probably other parts someone can chime in with.

[1] https://code.google.com/p/chromium/codesearch#chromium/src/s...

[2] http://www.chromium.org/developers/design-documents/sync