postmortem: export private field offsets

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 92f0ded0361bc0fa9e75374b96628e6d08096ba7..f56a688d30e2d510240e64d5d923b0eb78e40965 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -448,6 +448,7 @@ class HistogramTimer;
 class Isolate;
 class MemoryReducer;
 class ObjectStats;
+class PostMortem;
 class Scavenger;
 class ScavengeJob;
 class WeakObjectRetainer;
@@ -2373,6 +2374,9 @@ class Heap {
   // Used in cctest.
   friend class HeapTester;
 
+  // Used in postmortem.
+  friend class PostMortem;
+
   DISALLOW_COPY_AND_ASSIGN(Heap);
 };