Extending v8::GetHeapStatistics to return total available size.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index bca6bf1b6fd1c99f762ec307452661e0477d2300..208b557da682a073e9b66b7d9add15f056177e86 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -4776,6 +4776,7 @@ class V8_EXPORT HeapStatistics {
   size_t total_heap_size() { return total_heap_size_; }
   size_t total_heap_size_executable() { return total_heap_size_executable_; }
   size_t total_physical_size() { return total_physical_size_; }
+  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_; }
 
@@ -4783,6 +4784,7 @@ class V8_EXPORT HeapStatistics {
   size_t total_heap_size_;
   size_t total_heap_size_executable_;
   size_t total_physical_size_;
+  size_t total_available_size_;
   size_t used_heap_size_;
   size_t heap_size_limit_;