Display isolate message queue in Observatory debugger

runtime/vm/message.h

Index: runtime/vm/message.h
diff --git a/runtime/vm/message.h b/runtime/vm/message.h
index 3c08ae94ee3f7471cb7a3024b5e4e5db092c5441..42a1eb1e1a353a1bb681b27ba33b56aa29301d57 100644
--- a/runtime/vm/message.h
+++ b/runtime/vm/message.h
@@ -6,6 +6,7 @@
 #define VM_MESSAGE_H_
 
 #include "platform/assert.h"
+#include "vm/allocation.h"
 #include "vm/globals.h"
 
 // Duplicated from dart_api.h to avoid including the whole header.
@@ -13,6 +14,8 @@ typedef int64_t Dart_Port;
 
 namespace dart {
 
+class JSONStream;
+
 class Message {
  public:
   typedef enum {
@@ -68,6 +71,10 @@ class Message {
 
   bool RedirectToDeliveryFailurePort();
 
+  intptr_t Id() const;
+
+  static const char* PriorityAsString(Priority priority);
+
  private:
   friend class MessageQueue;
 
@@ -98,6 +105,31 @@ class MessageQueue {
   // Clear all messages from the message queue.
   void Clear();
 
+  // Iterator class.
+  class Iterator : public ValueObject {
+   public:
+    explicit Iterator(const MessageQueue* queue);
+    virtual ~Iterator();
+
+    void Reset(const MessageQueue* queue);
+
+    // Returns false when there are no more messages left.
+    bool HasNext();
+
+    // Returns the current message and moves forward.
+    Message* Next();
+
+   private:
+    Message* next_;
+  };
+
+  intptr_t Length() const;
+
+  // Returns the message with id or NULL.
+  Message* FindMessageById(intptr_t id);
+
+  void PrintJSON(JSONStream* stream);
+
  private:
   Message* head_;
   Message* tail_;