Make PopSirt inlinable, pass self to SirtRef.

Change-Id: Ieb91526b1cb1f8644ceb3c5b99649f658f43bbc1
diff --git a/src/heap.h b/src/heap.h
index 0a054e2..76206c4 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -301,7 +301,7 @@
   void EnqueueClearedReferences(Object** cleared_references);
 
   void RequestHeapTrim();
-  void RequestConcurrentGC();
+  void RequestConcurrentGC(Thread* self);
 
   // Swap bitmaps (if we are a full Gc then we swap the zygote bitmap too).
   void SwapBitmaps(Thread* self) EXCLUSIVE_LOCKS_REQUIRED(GlobalSynchronization::heap_bitmap_lock_);