Added a missing #include.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@43477 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/clang/AST/StmtIterator.h b/include/clang/AST/StmtIterator.h
index 295db7f..207e4ed 100644
--- a/include/clang/AST/StmtIterator.h
+++ b/include/clang/AST/StmtIterator.h
@@ -15,6 +15,7 @@
 #define LLVM_CLANG_AST_STMT_ITR_H
 
 #include "llvm/ADT/iterator"
+#include <cassert>
 
 namespace clang {