We don't sync policy-installed extension data (which is by design, to avoid installing policy extensions across all a user's devices).  However, if a user started using an extension *before* it was required by policy, and then the extension migrates to a policy-installed extension, the data in sync is kept from its previous state.  What's more, this data cannot be updated, because the extension is unsyncable.  This led to issue 629927.

We should handle this somehow.  Unfortunately, it's unclear exactly how.  We could hypothetically blow away all the stored sync data, but that might be bad if the user *also* uses it when it's not policy-installed.  The best solution may be to just avoid the sync data if the extension is policy-installed.  But that can also be a bit complicated since the extension preferences can sync before the extension itself is installed, in which case we might not know for sure if it's policy installed or not.

cc'ing a bunch of folks who may be interested or have ideas.