Begin implementing a debugger page in Observatory.

runtime/bin/vmservice/observatory/lib/src/app/application.dart

Index: runtime/bin/vmservice/observatory/lib/src/app/application.dart
diff --git a/runtime/bin/vmservice/observatory/lib/src/app/application.dart b/runtime/bin/vmservice/observatory/lib/src/app/application.dart
index a848c35ee4dd8ab52e41c9441045d2fe81ffbcbe..891c53b6661e0b3038da5e060ddb98396f35508f 100644
--- a/runtime/bin/vmservice/observatory/lib/src/app/application.dart
+++ b/runtime/bin/vmservice/observatory/lib/src/app/application.dart
@@ -100,8 +100,8 @@ class ObservatoryApplication extends Observable {
   }
 
   void _registerPages() {
-    // Register ClassTreePage.
     _pageRegistry.add(new ClassTreePage(this));
+    _pageRegistry.add(new DebuggerPage(this));
     _pageRegistry.add(new VMConnectPage(this));
     _pageRegistry.add(new ErrorViewPage(this));
     _pageRegistry.add(new MetricsPage(this));