heap: allow allocation in gc prologue/epilogue

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index dd8f2685bc37115638f5332ddbefd42a79c16cea..6b7b6dfaab97ae824886b3872a09230f64dcbec9 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -4127,13 +4127,12 @@ class V8_EXPORT Isolate {
 
   /**
    * Enables the host application to receive a notification before a
-   * garbage collection.  Allocations are not allowed in the
-   * callback function, you therefore cannot manipulate objects (set
-   * or delete properties for example) since it is possible such
-   * operations will result in the allocation of objects. It is possible
-   * to specify the GCType filter for your callback. But it is not possible to
-   * register the same callback function two times with different
-   * GCType filters.
+   * garbage collection. Allocations are allowed in the callback function,
+   * but the callback is not re-entrant: if the allocation inside it will
+   * trigger the garbage collection, the callback won't be called again.
+   * It is possible to specify the GCType filter for your callback. But it is
+   * not possible to register the same callback function two times with
+   * different GCType filters.
    */
   void AddGCPrologueCallback(
       GCPrologueCallback callback, GCType gc_type_filter = kGCTypeAll);
@@ -4146,13 +4145,12 @@ class V8_EXPORT Isolate {
 
   /**
    * Enables the host application to receive a notification after a
-   * garbage collection.  Allocations are not allowed in the
-   * callback function, you therefore cannot manipulate objects (set
-   * or delete properties for example) since it is possible such
-   * operations will result in the allocation of objects. It is possible
-   * to specify the GCType filter for your callback. But it is not possible to
-   * register the same callback function two times with different
-   * GCType filters.
+   * garbage collection. Allocations are allowed in the callback function,
+   * but the callback is not re-entrant: if the allocation inside it will
+   * trigger the garbage collection, the callback won't be called again.
+   * It is possible to specify the GCType filter for your callback. But it is
+   * not possible to register the same callback function two times with
+   * different GCType filters.
    */
   void AddGCEpilogueCallback(
       GCEpilogueCallback callback, GCType gc_type_filter = kGCTypeAll);