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

runtime/observatory/lib/src/service/object.dart

Index: runtime/observatory/lib/src/service/object.dart
diff --git a/runtime/observatory/lib/src/service/object.dart b/runtime/observatory/lib/src/service/object.dart
index 246fba9f85110b8cdf473f2221350a625a9c0b3e..63e4e1009611aa82f2899ce5808f00264ef2d77d 100644
--- a/runtime/observatory/lib/src/service/object.dart
+++ b/runtime/observatory/lib/src/service/object.dart
@@ -895,6 +895,10 @@ abstract class VM extends ServiceObjectOwner implements M.VM {
     return invokeRpc('getFlagList', {});
   }
 
+  Future enableProfiler() {
+    return invokeRpc("_enableProfiler", {});
+  }
+
   Future<ServiceObject> _streamListen(String streamId) {
     Map params = {
       'streamId': streamId,