Introduce remote objects in Debugger protocol

runtime/vm/debugger.h

Index: runtime/vm/debugger.h
===================================================================
--- runtime/vm/debugger.h	(revision 7863)
+++ runtime/vm/debugger.h	(working copy)
@@ -14,8 +14,8 @@
 class Isolate;
 class ObjectPointerVisitor;
 class ActiveVariables;
+class RemoteObjectCache;
 
-
 // SourceBreakpoint represents a user-specified breakpoint location in
 // Dart source. There may be more than one CodeBreakpoint object per
 // SourceBreakpoint.
@@ -154,7 +154,7 @@
   intptr_t token_index_;
   intptr_t line_number_;
 
-  LocalVarDescriptors* var_descriptors_;
+  LocalVarDescriptors& var_descriptors_;
   ZoneGrowableArray<intptr_t> desc_indices_;
 
   friend class Debugger;
@@ -186,7 +186,6 @@
                                DebuggerStackTrace* stack);
 
 
-
 class Debugger {
  public:
   enum EventType {
@@ -240,6 +239,10 @@
   RawArray* GetInstanceFields(const Instance& obj);
   RawArray* GetStaticFields(const Class& cls);
 
+  intptr_t CacheObject(const Object& obj);
+  RawObject* GetCachedObject(intptr_t obj_id);
+  bool IsValidObjectId(intptr_t obj_id);
+
   // Utility functions.
   static const char* QualifiedFunctionName(const Function& func);
 
@@ -290,6 +293,8 @@
   // Current stack trace. Valid while executing breakpoint callback code.
   DebuggerStackTrace* stack_trace_;
 
+  RemoteObjectCache* obj_cache_;
+
   SourceBreakpoint* src_breakpoints_;
   CodeBreakpoint* code_breakpoints_;