[heap] Add compaction space.

src/heap/spaces.cc

Index: src/heap/spaces.cc
diff --git a/src/heap/spaces.cc b/src/heap/spaces.cc
index 8879d5e6021b64db80f1f27a8cbf567044f104fb..2625ecb1d0926596d517f8503248f5ca0812d78d 100644
--- a/src/heap/spaces.cc
+++ b/src/heap/spaces.cc
@@ -1003,6 +1003,42 @@ void PagedSpace::TearDown() {
 }
 
 
+void PagedSpace::MergeCompactionSpace(CompactionSpace* other) {
+  // Unmerged fields:
+  //   area_size_
+  //   allocation_info_
+  //   emergency_memory_
+  //   end_of_unswept_pages_
+  //   unswept_free_bytes_
+  //   anchor_
+
+  // It only makes sense to merge compatible spaces.
+  DCHECK(identity() == other->identity());
+
+  // Destroy the linear allocation space of {other}. This is needed to (a) not
+  // waste the memory and (b) keep the rest of the chunk in an iterable state
+  // (filler is needed).
+  int linear_size = static_cast<int>(other->limit() - other->top());
+  other->Free(other->top(), linear_size);
+
+  // Move over the free list.
+  free_list_.Concatenate(other->free_list());
+
+  // Update and clear accounting statistics.
+  accounting_stats_.Merge(other->accounting_stats_);
+  other->accounting_stats_.Clear();
+
+  // Move over pages.
+  PageIterator it(other);
+  Page* p = nullptr;
+  while (it.has_next()) {
+    p = it.next();
+    p->set_owner(this);
+    p->InsertAfter(anchor_.prev_page());
+  }
+}
+
+
 size_t PagedSpace::CommittedPhysicalMemory() {
   if (!base::VirtualMemory::HasLazyCommits()) return CommittedMemory();
   MemoryChunk::UpdateHighWaterMark(allocation_info_.top());