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

(cherry picked from commit 033aabf9)

Change-Id: Iaaf2954bcb67d21ae3df5d7ed3dcd86ed27c128a