Only watch location for BREAKPOINT event

This CL ensures we watch a location for BREAKPOINT event only. Other
events (single-step, method entry/exit, ...) are handled differently
and LocationOnly modifier is used as an event filter in this case.

This prevents from failing a check when we need to deoptimize for
non-breakpoint event.

Bug: 17908144
Change-Id: Ib413d62fa31480fec8d750543c0605ba52188350