[debugger] introduce abstract interface for break location.

src/debug/mips64/debug-mips64.cc

 // Copyright 2012 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_MIPS64
 
 #include "src/codegen.h"
 #include "src/debug/debug.h"
 
 namespace v8 {
@@ skipping 40 matching lines @@
   //   nop(DEBUG_BREAK_NOP)
   // to a call to the debug break slot code.
   //   li t9, address   (4-instruction sequence on mips64)
   //   call t9          (jalr t9 / nop instruction pair)
   patcher.masm()->li(v8::internal::t9,
                      Operand(reinterpret_cast<int64_t>(code->entry())),
                      ADDRESS_LOAD);
   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) {
   __ RecordComment("Debug break");
   {
     FrameScope scope(masm, StackFrame::INTERNAL);
 
     // Load padding words on stack.
     __ li(at, Operand(Smi::FromInt(LiveEdit::kFramePaddingValue)));
     __ Dsubu(sp, sp,
@@ skipping 65 matching lines @@
 
 
 const bool LiveEdit::kFrameDropperSupported = true;
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_MIPS64