Ignore soft heap limit when reserving space.

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index d205b9c96634f13663bdaf6578db3418f6f4dd74..0aacd841448c0a24581d1cafdf905d501b66a583 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -1342,6 +1342,10 @@ class Heap {
     return old_gen_allocation_limit_ - PromotedTotalSize();
   }
 
+  inline intptr_t OldGenerationCapacityAvailable() {
+    return max_old_generation_size_ - PromotedTotalSize();
+  }
+
   static const intptr_t kMinimumPromotionLimit = 5 * Page::kPageSize;
   static const intptr_t kMinimumAllocationLimit =
       8 * (Page::kPageSize > MB ? Page::kPageSize : MB);