Add --warn-on-pause-with-no-debugger flag. Add this to --observe behavior.

runtime/vm/isolate.cc

 // Copyright (c) 2013, 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 "vm/isolate.h"
 
 #include "include/dart_api.h"
 #include "include/dart_native_api.h"
 #include "platform/assert.h"
 #include "platform/text_buffer.h"
@@ skipping 66 matching lines @@
 // TODO(iposva): Make these isolate specific flags inaccessible using the
 // regular FLAG_xyz pattern.
 // These flags are per-isolate and only influence the defaults.
 DEFINE_FLAG(bool, enable_asserts, false, "Enable assert statements.");
 DEFINE_FLAG(bool, enable_type_checks, false, "Enable type checks.");
 DEFINE_FLAG(bool, error_on_bad_override, false,
             "Report error for bad overrides.");
 DEFINE_FLAG(bool, error_on_bad_type, false,
             "Report error for malformed types.");
 
+DECLARE_FLAG(bool, warn_on_pause_with_no_debugger);
+
 static void CheckedModeHandler(bool value) {
   FLAG_enable_asserts = value;
   FLAG_enable_type_checks = value;
 }
 
 // --enable-checked-mode and --checked both enable checked mode which is
 // equivalent to setting --enable-asserts and --enable-type-checks.
 DEFINE_FLAG_HANDLER(CheckedModeHandler,
                     enable_checked_mode,
                     "Enable checked mode.");
@@ skipping 465 matching lines @@
       status = ProcessUnhandledException(Error::Cast(result));
     } else {
       ASSERT(result.IsNull());
     }
   }
   return status;
 }
 
 
 void IsolateMessageHandler::NotifyPauseOnStart() {
-  if (Service::debug_stream.enabled()) {
+  if (Service::debug_stream.enabled() || FLAG_warn_on_pause_with_no_debugger) {
     StartIsolateScope start_isolate(I);
     StackZone zone(T);
     HandleScope handle_scope(T);
     ServiceEvent pause_event(I, ServiceEvent::kPauseStart);
     Service::HandleEvent(&pause_event);
   } else if (FLAG_trace_service) {
     OS::Print("vm-service: Dropping event of type PauseStart (%s)\n",
               I->name());
   }
 }
 
 
 void IsolateMessageHandler::NotifyPauseOnExit() {
-  if (Service::debug_stream.enabled()) {
+  if (Service::debug_stream.enabled() || FLAG_warn_on_pause_with_no_debugger) {
     StartIsolateScope start_isolate(I);
     StackZone zone(T);
     HandleScope handle_scope(T);
     ServiceEvent pause_event(I, ServiceEvent::kPauseExit);
     Service::HandleEvent(&pause_event);
   } else if (FLAG_trace_service) {
     OS::Print("vm-service: Dropping event of type PauseExit (%s)\n",
               I->name());
   }
 }
@@ skipping 1962 matching lines @@
 void IsolateSpawnState::DecrementSpawnCount() {
   ASSERT(spawn_count_monitor_ != NULL);
   ASSERT(spawn_count_ != NULL);
   MonitorLocker ml(spawn_count_monitor_);
   ASSERT(*spawn_count_ > 0);
   *spawn_count_ = *spawn_count_ - 1;
   ml.Notify();
 }
 
 }  // namespace dart