[debugger] introduce abstract interface for break location.

src/debug/arm64/debug-arm64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_ARM64
 
 #include "src/arm64/frames-arm64.h"
 #include "src/codegen.h"
 #include "src/debug/debug.h"
 
@@ skipping 56 matching lines @@
   patcher.b(&skip_constant);
   patcher.dc64(reinterpret_cast<int64_t>(code->entry()));
   patcher.bind(&skip_constant);
   // TODO(all): check the following is correct.
   // The debug break slot code will push a frame and call statically compiled
   // code. By using blr,  this call site will be registered in the frame.
   // The debugger can now iterate on the frames to find this call.
   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) {
   __ RecordComment("Debug break");
   Register scratch = x10;
   {
     FrameScope scope(masm, StackFrame::INTERNAL);
 
     // Load padding words on stack.
     __ Mov(scratch, Smi::FromInt(LiveEdit::kFramePaddingValue));
@@ skipping 65 matching lines @@
   __ Br(scratch);
 }
 
 
 const bool LiveEdit::kFrameDropperSupported = true;
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM64