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

runtime/vm/service_event.h

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_SERVICE_EVENT_H_
 #define VM_SERVICE_EVENT_H_
 
 #include "vm/debugger.h"
 
 class DebuggerEvent;
@@ skipping 11 matching lines @@
     kPauseExit,          // --pause-isolates-on-exit
     kPauseBreakpoint,
     kPauseInterrupted,
     kPauseException,
     kResume,
 
     kBreakpointAdded,
     kBreakpointResolved,
     kBreakpointRemoved,
 
+    kGC,
+
     kIllegal,
   };
 
   ServiceEvent(Isolate* isolate, EventType event_type)
       : isolate_(isolate),
         type_(event_type),
         breakpoint_(NULL),
         top_frame_(NULL),
-        exception_(NULL) {}
+        exception_(NULL),
+        gc_stats_(NULL) {}
 
   explicit ServiceEvent(const DebuggerEvent* debugger_event);
 
   Isolate* isolate() const { return isolate_; }
 
   EventType type() const { return type_; }
 
   SourceBreakpoint* breakpoint() const {
     return breakpoint_;
   }
@@ skipping 17 matching lines @@
   }
 
   const Object* exception() const {
     return exception_;
   }
   void set_exception(const Object* exception) {
     ASSERT(type_ == kPauseException);
     exception_ = exception;
   }
 
+  const Heap::GCStats* gc_stats() const {
+    return gc_stats_;
+  }
+
+  void set_gc_stats(const Heap::GCStats* gc_stats) {
+    gc_stats_ = gc_stats;
+  }
+
   void PrintJSON(JSONStream* js) const;
 
   static const char* EventTypeToCString(EventType type);
 
  private:
   Isolate* isolate_;
   EventType type_;
   SourceBreakpoint* breakpoint_;
   ActivationFrame* top_frame_;
   const Object* exception_;
+  const Heap::GCStats* gc_stats_;
 };
 
 }  // namespace dart
 
 #endif  // VM_SERVICE_EVENT_H_