[Sync] Convert to using auto-generated ModelType.
See http://crrev.com/
1247853007 for where the new ModelType was added.
- ModelType is now just represented by an integer.
- ModelType is now located in org.chromium.sync.
- Many of the constants were singular and are now plural to match
the ones in model_type.h.
- ModelTypeSet is removed and a jintArray is used for JNI.
BUG=509788
TBR=thestig@chromium.org
Review URL: https://codereview.chromium.org/
1262413006
Cr-Commit-Position: refs/heads/master@{#343051}