Fixed missing method referenced when MallocHooks is unsupported.

runtime/observatory/lib/elements.dart

Index: runtime/observatory/lib/elements.dart
diff --git a/runtime/observatory/lib/elements.dart b/runtime/observatory/lib/elements.dart
index 903d5fcb95b89f39154f48c1df89db3cf7840510..50badc3efc4946c5da2309d186869296e2b46c85 100644
--- a/runtime/observatory/lib/elements.dart
+++ b/runtime/observatory/lib/elements.dart
@@ -52,6 +52,7 @@ import 'package:observatory/src/elements/megamorphiccache_view.dart';
 import 'package:observatory/src/elements/metric/details.dart';
 import 'package:observatory/src/elements/metric/graph.dart';
 import 'package:observatory/src/elements/metrics.dart';
+import 'package:observatory/src/elements/native_memory_profiler.dart';
 import 'package:observatory/src/elements/nav/class_menu.dart';
 import 'package:observatory/src/elements/nav/isolate_menu.dart';
 import 'package:observatory/src/elements/nav/library_menu.dart';
@@ -148,6 +149,7 @@ export 'package:observatory/src/elements/megamorphiccache_view.dart';
 export 'package:observatory/src/elements/metric/details.dart';
 export 'package:observatory/src/elements/metric/graph.dart';
 export 'package:observatory/src/elements/metrics.dart';
+export 'package:observatory/src/elements/native_memory_profiler.dart';
 export 'package:observatory/src/elements/nav/class_menu.dart';
 export 'package:observatory/src/elements/nav/isolate_menu.dart';
 export 'package:observatory/src/elements/nav/library_menu.dart';
@@ -248,6 +250,7 @@ Future initElements() async {
   MetricDetailsElement.tag.ensureRegistration();
   MetricGraphElement.tag.ensureRegistration();
   MetricsPageElement.tag.ensureRegistration();
+  NativeMemoryProfileElement.tag.ensureRegistration();
   NavClassMenuElement.tag.ensureRegistration();
   NavIsolateMenuElement.tag.ensureRegistration();
   NavLibraryMenuElement.tag.ensureRegistration();