Track external allocated memory for weak persistent handles.

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
===================================================================
--- runtime/include/dart_api.h	(revision 33235)
+++ runtime/include/dart_api.h	(working copy)
@@ -434,6 +434,8 @@
  * \param object An object.
  * \param peer A pointer to a native object or NULL.  This value is
  *   provided to callback when it is invoked.
+ * \param external_allocation_size The number of externally allocated
+ *   bytes for peer. Used to inform the garbage collector.
  * \param callback A function pointer that will be invoked sometime
  *   after the object is garbage collected.
  *
@@ -443,6 +445,7 @@
 DART_EXPORT Dart_WeakPersistentHandle Dart_NewWeakPersistentHandle(
     Dart_Handle object,
     void* peer,
+    intptr_t external_allocation_size,
     Dart_WeakPersistentHandleFinalizer callback);
 
 DART_EXPORT void Dart_DeleteWeakPersistentHandle(
@@ -468,6 +471,8 @@
  * \param object An object.
  * \param peer A pointer to a native object or NULL.  This value is
  *   provided to callback when it is invoked.
+ * \param external_allocation_size The number of externally allocated
+ *   bytes for peer. Used to inform the garbage collector.
  * \param callback A function pointer that will be invoked sometime
  *   after the object is garbage collected.
  *
@@ -477,6 +482,7 @@
 DART_EXPORT Dart_WeakPersistentHandle Dart_NewPrologueWeakPersistentHandle(
     Dart_Handle object,
     void* peer,
+    intptr_t external_allocation_size,
     Dart_WeakPersistentHandleFinalizer callback);
 
 /**