[heap] Respect max_pages argument in ParallelSweepSpace

Increment pages_freed each time a page was swept. Before pages_freed
was always 0, which meant that the max_pages-argument did not have any
effect.

Change-Id: Id8908bdeb38e262e09b4069893f8f81209568080
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1872399Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64564}

src/heap/sweeper.cc

@@ -436,6 +436,7 @@ int Sweeper::ParallelSweepSpace(
   while ((page = GetSweepingPageSafe(identity)) != nullptr) {
     int freed =
         ParallelSweepPage(page, identity, invalidated_slots_in_free_space);
+    ++pages_freed;
     if (page->IsFlagSet(Page::NEVER_ALLOCATE_ON_PAGE)) {
       // Free list of a never-allocate page will be dropped later on.
       continue;