Do not JSON encode the 'result' of a service rpc.

runtime/vm/heap.h

Index: runtime/vm/heap.h
diff --git a/runtime/vm/heap.h b/runtime/vm/heap.h
index cd28cd6458b5d133ee64af1a78529325273ce71c..928e7c5c8cf76e4b23ea64e564d43d02c96351b6 100644
--- a/runtime/vm/heap.h
+++ b/runtime/vm/heap.h
@@ -21,6 +21,7 @@ namespace dart {
 class Isolate;
 class ObjectPointerVisitor;
 class ObjectSet;
+class ServiceEvent;
 class VirtualMemory;
 
 DECLARE_FLAG(bool, verbose_gc);
@@ -312,22 +313,12 @@ class Heap {
 
   int pretenure_policy_;
 
-  friend class GCEvent;
+  friend class ServiceEvent;
   friend class GCTestHelper;
   DISALLOW_COPY_AND_ASSIGN(Heap);
 };
 
 
-class GCEvent {
- public:
-  explicit GCEvent(const Heap::GCStats& stats)
-      : stats_(stats) {}
-  void PrintJSON(JSONStream* js) const;
- private:
-  const Heap::GCStats& stats_;
-};
-
-
 // Within a NoSafepointScope, the thread must not reach any safepoint. Used
 // around code that manipulates raw object pointers directly without handles.
 #if defined(DEBUG)