Rework service extensions to be safe

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index 3d06d6f091662382d079c13919042702373feb7c..74ba3d92ab8b90466664a0682250d205aaf82ca5 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -707,6 +707,14 @@ class Isolate : public BaseIsolate {
     compilation_allowed_ = allowed;
   }
 
+  RawGrowableObjectArray* pending_extension_calls() const {
+    return pending_extension_calls_;
+  }
+  void set_pending_extension_calls(const GrowableObjectArray& value);

[turnidge, 2015/08/20 17:34:39]

Maybe make pending_extension_calls, set_pending_extension_calls, and
PrunePendingExtensionCalls private.

[Cutch, 2015/08/20 18:09:37]

Done.

+  RawObject* InvokePendingExtensionCalls();
+  RawGrowableObjectArray* PrunePendingExtensionCalls();
+  void AppendExtensionCall(const Instance& closure);
+
 #if defined(DEBUG)
 #define REUSABLE_HANDLE_SCOPE_ACCESSORS(object)                                \
   void set_reusable_##object##_handle_scope_active(bool value) {               \
@@ -861,6 +869,8 @@ class Isolate : public BaseIsolate {
   RawGrowableObjectArray* collected_closures_;
   RawGrowableObjectArray* deoptimized_code_array_;
 
+  RawGrowableObjectArray* pending_extension_calls_;
+
   Metric* metrics_list_head_;
 
   Counters counters_;