2nd attempt at adding streamListen/streamCancel to the service protocol.

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 "platform/assert.h"
 #include "platform/json.h"
 #include "vm/code_observers.h"
@@ skipping 432 matching lines @@
     } else {
       ASSERT(result.IsNull());
     }
   }
   delete message;
   return success;
 }
 
 
 void IsolateMessageHandler::NotifyPauseOnStart() {
-  StartIsolateScope start_isolate(isolate());
-  StackZone zone(I);
-  HandleScope handle_scope(I);
-  ServiceEvent pause_event(isolate(), ServiceEvent::kPauseStart);
-  Service::HandleEvent(&pause_event);
+  if (Service::NeedsDebugEvents()) {
+    StartIsolateScope start_isolate(isolate());
+    StackZone zone(I);
+    HandleScope handle_scope(I);
+    ServiceEvent pause_event(isolate(), ServiceEvent::kPauseStart);
+    Service::HandleEvent(&pause_event);
+  }
 }
 
 
 void IsolateMessageHandler::NotifyPauseOnExit() {
-  StartIsolateScope start_isolate(isolate());
-  StackZone zone(I);
-  HandleScope handle_scope(I);
-  ServiceEvent pause_event(isolate(), ServiceEvent::kPauseExit);
-  Service::HandleEvent(&pause_event);
+  if (Service::NeedsDebugEvents()) {
+    StartIsolateScope start_isolate(isolate());
+    StackZone zone(I);
+    HandleScope handle_scope(I);
+    ServiceEvent pause_event(isolate(), ServiceEvent::kPauseExit);
+    Service::HandleEvent(&pause_event);
+  }
 }
 
 
 #if defined(DEBUG)
 void IsolateMessageHandler::CheckAccess() {
   ASSERT(IsCurrentIsolate());
 }
 #endif
 
 
@@ skipping 1484 matching lines @@
                            serialized_message_, serialized_message_len_);
 }
 
 
 void IsolateSpawnState::Cleanup() {
   SwitchIsolateScope switch_scope(I);
   Dart::ShutdownIsolate();
 }
 
 }  // namespace dart