Reuse RelocInfo's IsPatchedDebugBreakSlotSequence() implementation.

RelocInfo::IsPatchedDebugBreakSlotSequence() already does this assembly
check, so just reuse it in BreakLocationIterator::IsDebugBreakAtSlot(),
like the other debug ports do.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/321743002

Patch from Thiago Farina <tfarina@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21734 ce2b1a6d-e550-0410-aec6-3dcde31c8c00