[debugger] introduce abstract interface for break location.

src/debug/arm64/debug-arm64.cc

Index: src/debug/arm64/debug-arm64.cc
diff --git a/src/debug/arm64/debug-arm64.cc b/src/debug/arm64/debug-arm64.cc
index c2b60a9326be95ec970d26b49cf3ff7d839d88e7..3e4b67c93881d62a5ce68f41e387c385d9f4d0a0 100644
--- a/src/debug/arm64/debug-arm64.cc
+++ b/src/debug/arm64/debug-arm64.cc
@@ -74,6 +74,10 @@ void DebugCodegen::PatchDebugBreakSlot(Isolate* isolate, Address pc,
   patcher.blr(ip0);
 }
 
+bool DebugCodegen::DebugBreakSlotIsPatched(Address pc) {
+  Instruction* current_instr = reinterpret_cast<Instruction*>(pc);
+  return !current_instr->IsNop(Assembler::DEBUG_BREAK_NOP);
+}
 
 void DebugCodegen::GenerateDebugBreakStub(MacroAssembler* masm,
                                           DebugBreakCallHelperMode mode) {