Make safe label more safe
* limit the absolute maximum size of the label to 50000 characters
[which is probably far more than necessary, but, can be dialed down]
* use a string buffer while processing the string [instead of creating
multiple string objects]
Bug:
62537081
Test: Manual. Install APK in bug and see that it can be uninstalled
Change-Id: Ibf63c2691ad7438a123e92110d95b1f50050f8b1
Merged-In: Ibf63c2691ad7438a123e92110d95b1f50050f8b1
(cherry picked from commit
2263da9539daef134395226a2718ba2d7af7547d)