[heap] Enforce safepoint in unittest when iterating chunks

HeapWithPointerCompressionTest.HeapLayout sometimes raced with
background threads. When iterating chunks, background threads might add
chunks concurrently. Prevent this by enforcing safepoint during
iteration.

Bug: v8:10315
Change-Id: I2852ec3ea18905b669e60eadc660d9343ea35f48
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2390767
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69696}

test/unittests/heap/heap-unittest.cc

@@ -10,6 +10,7 @@
 
 #include "src/handles/handles-inl.h"
 #include "src/heap/memory-chunk.h"
+#include "src/heap/safepoint.h"
 #include "src/heap/spaces-inl.h"
 #include "src/objects/objects-inl.h"
 #include "test/unittests/test-utils.h"
@@ -151,6 +152,7 @@ TEST_F(HeapWithPointerCompressionTest, HeapLayout) {
   // Check that all memory chunks belong this region.
   base::AddressRegion heap_reservation(isolate_root, size_t{4} * GB);
 
+  SafepointScope scope(i_isolate()->heap());
   OldGenerationMemoryChunkIterator iter(i_isolate()->heap());
   for (;;) {
     MemoryChunk* chunk = iter.next();