Use a lock in pages to synchronize sweeper threads to allow others to wait on concurrently swept pa…

src/heap/spaces-inl.h

Index: src/heap/spaces-inl.h
diff --git a/src/heap/spaces-inl.h b/src/heap/spaces-inl.h
index c2c4d126976336dd4348d0e76c4575b3f9748218..f2bdbfcfa0aaf561b9fa8382633731e335204834 100644
--- a/src/heap/spaces-inl.h
+++ b/src/heap/spaces-inl.h
@@ -142,6 +142,7 @@ void MemoryAllocator::UnprotectChunkFromPage(Page* page) {
 Page* Page::Initialize(Heap* heap, MemoryChunk* chunk, Executability executable,
                        PagedSpace* owner) {
   Page* page = reinterpret_cast<Page*>(chunk);
+  page->mutex_ = new base::Mutex();
   DCHECK(page->area_size() <= kMaxRegularHeapObjectSize);
   DCHECK(chunk->owner() == owner);
   owner->IncreaseCapacity(page->area_size());