[not for landing, heap] Parallel compaction in main GC pause

src/heap/mark-compact.h

Index: src/heap/mark-compact.h
diff --git a/src/heap/mark-compact.h b/src/heap/mark-compact.h
index e0b7c38ca0bd0cfc2c0f785b31c59c476a576943..db7289aa99f8db6fe534e152e0bae22141624bc8 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -556,6 +556,8 @@ class MarkCompactCollector {
   // Synchronize compaction threads.
   base::Semaphore pending_compaction_jobs_semaphore_;
 
+  size_t concurrent_compaction_tasks_active_;
+
   bool evacuation_;
 
   SlotsBufferAllocator* slots_buffer_allocator_;
@@ -713,8 +715,11 @@ class MarkCompactCollector {
   void EvacuateNewSpace();
 
   void EvacuateLiveObjectsFromPage(Page* p, PagedSpace* target_space);
+  bool EvacuateLiveObjectsFromPageWithoutEmergency(Page* p,
+                                                   PagedSpace* target_space);
 
   void EvacuatePages();
+  void EvacuatePagesUsingCompactionSpace(CompactionSpaces* compaction_spaces);
 
   void EvacuatePagesInParallel();