Use atomic operation to read the length of a fixed array.

test/cctest/test-heap.cc

Index: test/cctest/test-heap.cc
diff --git a/test/cctest/test-heap.cc b/test/cctest/test-heap.cc
index 0d668c8b94b4307ef2457f836227ba8bd67ee587..c8515418d7d7b5c9496102f0c8d2f70f85dd1c30 100644
--- a/test/cctest/test-heap.cc
+++ b/test/cctest/test-heap.cc
@@ -5328,7 +5328,8 @@ static void TestRightTrimFixedTypedArray(v8::ExternalArrayType type,
   Handle<FixedTypedArrayBase> array =
       factory->NewFixedTypedArray(initial_length, type);
   int old_size = array->size();
-  heap->RightTrimFixedArray<Heap::FROM_MUTATOR>(*array, elements_to_trim);
+  heap->RightTrimFixedArray<Heap::CONCURRENT_TO_SWEEPER>(*array,
+                                                         elements_to_trim);
 
   // Check that free space filler is at the right place and did not smash the
   // array header.