[vm] Don't enable the profiler by default. Enable the profiler at startup with --observe, or later …

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 <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include "include/dart_api.h"
 #include "include/dart_tools_api.h"
@@ skipping 438 matching lines @@
           DEFAULT_VM_SERVICE_SERVER_PORT, DEFAULT_VM_SERVICE_SERVER_IP)) {
     Log::PrintErr(
         "unrecognized --observe option syntax. "
         "Use --observe[=<port number>[/<bind address>]]\n");
     return false;
   }
 
   // These options should also be documented in the help message.
   vm_options->AddArgument("--pause-isolates-on-exit");
   vm_options->AddArgument("--pause-isolates-on-unhandled-exceptions");
+  vm_options->AddArgument("--profiler");
   vm_options->AddArgument("--warn-on-pause-with-no-debugger");
   return true;
 }
 
 static bool ProcessTraceLoadingOption(const char* arg,
                                       CommandLineOptions* vm_options) {
   if (*arg != '\0') {
     return false;
   }
   trace_loading = true;
@@ skipping 1435 matching lines @@
   Platform::Exit(Process::GlobalExitCode());
 }
 
 }  // namespace bin
 }  // namespace dart
 
 int main(int argc, char** argv) {
   dart::bin::main(argc, argv);
   UNREACHABLE();
 }