Revert of [debugger api] remove legacy JSON debug protocol.

src/execution.cc

 // Copyright 2014 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.
 
 #include "src/execution.h"
 
 #include "src/bootstrapper.h"
 #include "src/codegen.h"
 #include "src/compiler-dispatcher/optimizing-compile-dispatcher.h"
 #include "src/isolate-inl.h"
@@ skipping 451 matching lines @@
 Object* StackGuard::HandleInterrupts() {
   if (FLAG_verify_predictable) {
     // Advance synthetic time by making a time request.
     isolate_->heap()->MonotonicallyIncreasingTimeInMs();
   }
 
   if (CheckAndClearInterrupt(GC_REQUEST)) {
     isolate_->heap()->HandleGCRequest();
   }
 
-  if (CheckDebugBreak()) {
+  if (CheckDebugBreak() || CheckDebugCommand()) {
     isolate_->debug()->HandleDebugBreak();
   }
 
   if (CheckAndClearInterrupt(TERMINATE_EXECUTION)) {
     return isolate_->TerminateExecution();
   }
 
   if (CheckAndClearInterrupt(DEOPT_MARKED_ALLOCATION_SITES)) {
     isolate_->heap()->DeoptMarkedAllocationSites();
   }
@@ skipping 10 matching lines @@
 
   isolate_->counters()->stack_interrupts()->Increment();
   isolate_->counters()->runtime_profiler_ticks()->Increment();
   isolate_->runtime_profiler()->MarkCandidatesForOptimization();
 
   return isolate_->heap()->undefined_value();
 }
 
 }  // namespace internal
 }  // namespace v8