Expose a lower bound of malloc'd memory via heap statistics

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index db2178b73becb2c7ad76a5f28e8b81e4c14d1c33..73c179189331d345c2aa54aa530c7d0c2142051e 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -5177,6 +5177,7 @@ class V8_EXPORT HeapStatistics {
   size_t total_available_size() { return total_available_size_; }
   size_t used_heap_size() { return used_heap_size_; }
   size_t heap_size_limit() { return heap_size_limit_; }
+  size_t malloced_memory() { return malloced_memory_; }
   size_t does_zap_garbage() { return does_zap_garbage_; }
 
  private:
@@ -5186,6 +5187,7 @@ class V8_EXPORT HeapStatistics {
   size_t total_available_size_;
   size_t used_heap_size_;
   size_t heap_size_limit_;
+  size_t malloced_memory_;
   bool does_zap_garbage_;
 
   friend class V8;