Handle null isolate case in service tracing

runtime/vm/service.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/service.h"
 
 #include "include/dart_api.h"
 #include "include/dart_native_api.h"
 #include "platform/globals.h"
 
@@ skipping 719 matching lines @@
   stream_id_cobj.value.as_string = const_cast<char*>(stream_id);
   list_values[0] = &stream_id_cobj;
 
   Dart_CObject json_cobj;
   json_cobj.type = Dart_CObject_kString;
   json_cobj.value.as_string = const_cast<char*>(event->ToCString());
   list_values[1] = &json_cobj;
 
   if (FLAG_trace_service) {
     Isolate* isolate = Isolate::Current();
-    ASSERT(isolate != NULL);
+    const char* isolate_name = "<no current isolate>";
+    if (isolate != NULL) {
+      isolate_name = isolate->name();
+    }
     OS::Print(
         "vm-service: Pushing event of type %s to stream %s (%s)\n",
-        kind, stream_id, isolate->name());
+        kind, stream_id, isolate_name);
   }
 
   Dart_PostCObject(ServiceIsolate::Port(), &list_cobj);
 }
 
 
 class EmbedderServiceHandler {
  public:
   explicit EmbedderServiceHandler(const char* name) : name_(NULL),
                                                       callback_(NULL),
@@ skipping 2385 matching lines @@
     ServiceMethodDescriptor& method = service_methods_[i];
     if (strcmp(method_name, method.name) == 0) {
       return &method;
     }
   }
   return NULL;
 }
 
 
 }  // namespace dart