[debugger] introduce abstract interface for break location.

src/debug/mips64/debug-mips64.cc

Index: src/debug/mips64/debug-mips64.cc
diff --git a/src/debug/mips64/debug-mips64.cc b/src/debug/mips64/debug-mips64.cc
index 1d65fd9efdedebf53f781d2db31872f86bd39607..0646a249f7a92e2a512c91fd87cb7c800b4f092e 100644
--- a/src/debug/mips64/debug-mips64.cc
+++ b/src/debug/mips64/debug-mips64.cc
@@ -58,6 +58,10 @@ void DebugCodegen::PatchDebugBreakSlot(Isolate* isolate, Address pc,
   patcher.masm()->Call(v8::internal::t9);
 }
 
+bool DebugCodegen::DebugBreakSlotIsPatched(Address pc) {
+  Instr current_instr = Assembler::instr_at(pc);
+  return !Assembler::IsNop(current_instr, Assembler::DEBUG_BREAK_NOP);
+}
 
 void DebugCodegen::GenerateDebugBreakStub(MacroAssembler* masm,
                                           DebugBreakCallHelperMode mode) {