Send the GC's SIGQUIT output to the right ostream.

I'm not convinced the GC should be quite as verbose as it is for SIGQUIT,
but it should definitely send the output to the correct destination.

Change-Id: I7095cf8255540fc4a5014f53d7dfc0bc38c51843
diff --git a/src/heap.h b/src/heap.h
index a2c2d98..642c436 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -332,7 +332,7 @@
   void UnReserveOatFileAddressRange();
 
   // GC performance measuring
-  void DumpGcPerformanceInfo();
+  void DumpGcPerformanceInfo(std::ostream& os);
 
   // Thread pool.
   void CreateThreadPool();