[debugger] introduce abstract interface for break location.

src/debug/mips/debug-mips.cc

Index: src/debug/mips/debug-mips.cc
diff --git a/src/debug/mips/debug-mips.cc b/src/debug/mips/debug-mips.cc
index c5c58d044b0cd522caf1d31e9a8b3e5ac6602015..1d9f7d603705700adc7821a44d14c93471b497db 100644
--- a/src/debug/mips/debug-mips.cc
+++ b/src/debug/mips/debug-mips.cc
@@ -56,6 +56,10 @@ 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) {