Support garbage collection of JITted code.

Change-Id: I9afc544460ae4fb31149644b6196ac7f5182c784
diff --git a/runtime/linear_alloc.h b/runtime/linear_alloc.h
index 1b21527..df7f17d 100644
--- a/runtime/linear_alloc.h
+++ b/runtime/linear_alloc.h
@@ -47,6 +47,10 @@
   // Return true if the linear alloc contrains an address.
   bool Contains(void* ptr) const REQUIRES(!lock_);
 
+  // Unsafe version of 'Contains' only to be used when the allocator is going
+  // to be deleted.
+  bool ContainsUnsafe(void* ptr) const NO_THREAD_SAFETY_ANALYSIS;
+
  private:
   mutable Mutex lock_ DEFAULT_MUTEX_ACQUIRED_AFTER;
   ArenaAllocator allocator_ GUARDED_BY(lock_);