Clear native pointers when destroy()ing Java objects.
We weren't clearing the native pointers for these Java objects, but we
were asserting that the native pointers were 0 in the (evil) Java
finalizers. This resulted in an error in the logs (but no crash, thanks
to the beauty of finalizers).
NOTRY=true
Committed:
https://src.chromium.org/viewvc/chrome?view=rev&revision=236808