Implement prologue weak persistent handles.

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
diff --git a/runtime/include/dart_api.h b/runtime/include/dart_api.h
index 031c5668e6e602859a2fcf3be376d323caea3c18..84d766e248084b9e4fed2c46185bf579d83be467 100755
--- a/runtime/include/dart_api.h
+++ b/runtime/include/dart_api.h
@@ -251,6 +251,30 @@ DART_EXPORT Dart_Handle Dart_NewWeakPersistentHandle(
  */
 DART_EXPORT bool Dart_IsWeakPersistentHandle(Dart_Handle object);
 
+/**
+ * Allocates a prologue weak persistent handle for an object.
+ *
+ * Prologue weak persistent handles are similar to weak persistent
+ * handles.  However, prologue weak persistent handlers are only weak
+ * when the a garbage collector chooses to invoke the prologue and
+ * epilogue callbacks.

[siva, 2012/03/09 21:48:41]

I like the description you used in the gcl upload comments.

(These handles strongly reference their referent except in those garbage
collection cycles where the prolog/epilog callbacks are called).

[cshapiro, 2012/03/13 23:06:43]

I replaced the comment above with the description from the check-in.  Let me
know if that is okay.

+ *

[siva, 2012/03/09 21:48:41]

Documentation for parameters 'object, peer, callback'.
Also needs to be done for Dart_NewWeakPersistentHandle.

[cshapiro, 2012/03/13 23:06:43]

Done.

+ * This handle has the lifetime of the current isolate unless it is
+ * explicitly deallocated by calling Dart_DeletePersistentHandle.
+ *
+ * Requires there to be a current isolate.
+ */
+DART_EXPORT Dart_Handle Dart_NewPrologueWeakPersistentHandle(
+    Dart_Handle object,
+    void* peer,
+    Dart_WeakPersistentHandleFinalizer callback);
+
+/**
+ * Is this object a prologue weak persistent handle?
+ *
+ * Requires there to be a current isolate.
+ */
+DART_EXPORT bool Dart_IsPrologueWeakPersistentHandle(Dart_Handle object);
 
 /**
  * Constructs a set of weak references from the Cartesian product of