Print and save JS stacktrace on OOM crash.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 8574d55993d9dc523dc233170b3c667ebefe7c26..e4a656333fa169a78b9276fa8dad00631cae49f4 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1157,6 +1157,7 @@ class Heap {
       256 * kPointerMultiplier;
 
   static const int kTraceRingBufferSize = 512;
+  static const int kStacktraceBufferSize = 512;
 
   // Calculates the allocation limit based on a given growing factor and a
   // given old generation size.
@@ -2333,7 +2334,8 @@ class HeapStats {
   int* size_per_type;                      // 18
   int* os_error;                           // 19
   char* last_few_messages;                 // 20
-  int* end_marker;                         // 21
+  char* js_stacktrace;                     // 21
+  int* end_marker;                         // 22
 };