[zone containers] Fix iteration of const ZoneChunkList

With the current attempt, trying to iterate a const ZoneChunkList doesn't even
compile. See the bug for more info.

R=marja@chromium.org

Bug: v8:6473
Change-Id: I8de7e887398be7ba5da14dc540dd40b30df2c3fe
Reviewed-on: https://chromium-review.googlesource.com/868332Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50675}

test/unittests/zone/zone-chunk-list-unittest.cc

@@ -202,5 +202,30 @@ TEST(ZoneChunkList, BigCopyToTest) {
   }
 }
 
+void TestForwardIterationOfConstList(
+    const ZoneChunkList<uintptr_t>& zone_chunk_list) {
+  size_t count = 0;
+
+  for (uintptr_t item : zone_chunk_list) {
+    EXPECT_EQ(static_cast<size_t>(item), count);
+    count++;
+  }
+
+  EXPECT_EQ(count, kItemCount);
+}
+
+TEST(ZoneChunkList, ConstForwardIterationTest) {
+  AccountingAllocator allocator;
+  Zone zone(&allocator, ZONE_NAME);
+
+  ZoneChunkList<uintptr_t> zone_chunk_list(&zone);
+
+  for (size_t i = 0; i < kItemCount; ++i) {
+    zone_chunk_list.push_back(static_cast<uintptr_t>(i));
+  }
+
+  TestForwardIterationOfConstList(zone_chunk_list);
+}
+
 }  // namespace internal
 }  // namespace v8