Reland "Check for semaphore alignment on posix platforms. (patchset #1 id:1 of https://codereview.c…

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 58bf2a502998b5ff62973105d566bc75f94ebefc..7f61e78ae228c793e020d5f405cc8594f2cafa24 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -461,8 +461,8 @@ class MarkCompactCollector {
     void PrepareToBeSweptPage(AllocationSpace space, Page* page);
 
     Heap* heap_;
-    base::Mutex mutex_;
     base::Semaphore pending_sweeper_tasks_semaphore_;
+    base::Mutex mutex_;
     SweptList swept_list_[kAllocationSpaces];
     SweepingList sweeping_list_[kAllocationSpaces];
     bool sweeping_in_progress_;
@@ -868,9 +868,6 @@ class MarkCompactCollector {
   // candidates.
   bool compacting_;
 
-  // Semaphore used to synchronize compaction tasks.
-  base::Semaphore pending_compaction_tasks_semaphore_;
-
   bool black_allocation_;
 
   Sweeper sweeper_;