[runtime/heap] Introduce CopyFixedArrayUpTo to match CopyFixedArrayAndGrow, copying to a smaller ar…

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 11ce656a2ef79810b74369c07ef3e3d3c35f8ae2..50a8689921c1db9e216e4e19ce88eb6d3a0bae6d 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1877,6 +1877,11 @@ class Heap {
   MUST_USE_RESULT AllocationResult
   CopyFixedArrayAndGrow(FixedArray* src, int grow_by, PretenureFlag pretenure);
 
+  // Make a copy of src, also grow the copy, and return the copy.
+  MUST_USE_RESULT AllocationResult CopyFixedArrayUpTo(FixedArray* src,
+                                                      int new_len,
+                                                      PretenureFlag pretenure);
+
   // Make a copy of src, set the map, and return the copy.
   MUST_USE_RESULT AllocationResult
       CopyFixedArrayWithMap(FixedArray* src, Map* map);