Begin migrating the vm service from a rest-style interface to a json-rpc style interface.

runtime/observatory/lib/src/elements/debugger.dart

Index: runtime/observatory/lib/src/elements/debugger.dart
diff --git a/runtime/observatory/lib/src/elements/debugger.dart b/runtime/observatory/lib/src/elements/debugger.dart
index 1515bffd31838c3f85543c1dce8e6ff5c69edb6c..f17bacb4a7a12f5d7e89b93e9439745c4848004b 100644
--- a/runtime/observatory/lib/src/elements/debugger.dart
+++ b/runtime/observatory/lib/src/elements/debugger.dart
@@ -45,9 +45,9 @@ class DebuggerStackElement extends ObservatoryElement {
   @published int activeFrame = 0;
 
   isolateChanged(oldValue) {
-    isolate.get('stacktrace').then((result) {
+    isolate.getStack().then((result) {
         stack = result;
-      });
+    });
   }
 
   DebuggerStackElement.created() : super.created();