Teach the Observatory about Contexts. Factor out object graph information from the instance view.

runtime/bin/vmservice/observatory/lib/elements.dart

Index: runtime/bin/vmservice/observatory/lib/elements.dart
diff --git a/runtime/bin/vmservice/observatory/lib/elements.dart b/runtime/bin/vmservice/observatory/lib/elements.dart
index 302c640edb643e36b0e9355b5994524411a7cdf6..51a85556c17df6243adb1ee2962d7451d9305a6a 100644
--- a/runtime/bin/vmservice/observatory/lib/elements.dart
+++ b/runtime/bin/vmservice/observatory/lib/elements.dart
@@ -8,6 +8,8 @@ export 'package:observatory/src/elements/class_tree.dart';
 export 'package:observatory/src/elements/class_view.dart';
 export 'package:observatory/src/elements/code_ref.dart';
 export 'package:observatory/src/elements/code_view.dart';
+export 'package:observatory/src/elements/context_ref.dart';
+export 'package:observatory/src/elements/context_view.dart';
 export 'package:observatory/src/elements/curly_block.dart';
 export 'package:observatory/src/elements/error_view.dart';
 export 'package:observatory/src/elements/eval_box.dart';