Add an option to trace the debug protocol to the dart binary:

runtime/bin/main.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
 
 #include "include/dart_api.h"
 #include "include/dart_debugger_api.h"
@@ skipping 207 matching lines @@
   }
   if (vm_service_server_port < 0) {
     Log::PrintErr("unrecognized --enable-vm-service option syntax. "
                     "Use --enable-vm-service[:<port number>]\n");
     return false;
   }
   start_vm_service = true;
   return true;
 }
 
+bool trace_debug_protocol = false;
+static bool ProcessTraceDebugProtocolOption(const char* arg) {
+  if (*arg != '\0') {
+    return false;
+  }
+  trace_debug_protocol = true;
+  return true;
+}
+
+
 static struct {
   const char* option_name;
   bool (*process)(const char* option);
 } main_options[] = {
   // Standard options shared with dart2js.
   { "--version", ProcessVersionOption },
   { "--help", ProcessHelpOption },
   { "-h", ProcessHelpOption },
   { "--verbose", ProcessVerboseOption },
   { "-v", ProcessVerboseOption },
   { "--package-root=", ProcessPackageRootOption },
   // VM specific options to the standalone dart program.
   { "--break-at=", ProcessBreakpointOption },
   { "--compile_all", ProcessCompileAllOption },
   { "--debug", ProcessDebugOption },
   { "--snapshot=", ProcessGenScriptSnapshotOption },
   { "--print-script", ProcessPrintScriptOption },
   { "--check-function-fingerprints", ProcessFingerprintedFunctions },
   { "--enable-vm-service", ProcessEnableVmServiceOption },
+  { "--trace-debug-protocol", ProcessTraceDebugProtocolOption },
   { NULL, NULL }
 };
 
 
 static bool ProcessMainOptions(const char* option) {
   int i = 0;
   const char* name = main_options[0].option_name;
   int option_length = strlen(option);
   while (name != NULL) {
     int length = strlen(name);
@@ skipping 676 matching lines @@
 
   return Process::GlobalExitCode();
 }
 
 }  // namespace bin
 }  // namespace dart
 
 int main(int argc, char** argv) {
   return dart::bin::main(argc, argv);
 }