Fix error message with --observe flag

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 284 matching lines @@
                         DEFAULT_VM_SERVICE_SERVER_IP)) {
     Log::PrintErr("unrecognized --enable-vm-service option syntax. "
                   "Use --enable-vm-service[:<port number>[/<IPv4 address>]]\n");
     return false;
   }
 
   start_vm_service = true;
   return true;
 }
 
+
 static bool ProcessObserveOption(const char* option_value,
                                  CommandLineOptions* vm_options) {
   ASSERT(option_value != NULL);
 
-  if (!ProcessEnableVmServiceOption(option_value, vm_options)) {
+  if (!ExtractPortAndIP(option_value,
+                        &vm_service_server_port,
+                        &vm_service_server_ip,
+                        DEFAULT_VM_SERVICE_SERVER_PORT,
+                        DEFAULT_VM_SERVICE_SERVER_IP)) {
+    Log::PrintErr("unrecognized --observe option syntax. "
+                  "Use --observe[:<port number>[/<IPv4 address>]]\n");
     return false;
   }
+
+  start_vm_service = true;
+
   vm_options->AddArgument("--pause-isolates-on-exit");
   return true;
 }
 
 
 bool trace_debug_protocol = false;
 static bool ProcessTraceDebugProtocolOption(const char* arg,
                                             CommandLineOptions* vm_options) {
   if (*arg != '\0') {
     return false;
@@ skipping 834 matching lines @@
   exit(Process::GlobalExitCode());
 }
 
 }  // namespace bin
 }  // namespace dart
 
 int main(int argc, char** argv) {
   dart::bin::main(argc, argv);
   UNREACHABLE();
 }