Initialize the ASTMutationListener. Thanks goes to Abramo Bagnara!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@117541 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/ASTContext.cpp b/lib/AST/ASTContext.cpp
index 23e07af..99023ee 100644
--- a/lib/AST/ASTContext.cpp
+++ b/lib/AST/ASTContext.cpp
@@ -166,7 +166,7 @@
   Idents(idents), Selectors(sels),
   BuiltinInfo(builtins),
   DeclarationNames(*this),
-  ExternalSource(0), PrintingPolicy(LOpts),
+  ExternalSource(0), Listener(0), PrintingPolicy(LOpts),
   LastSDM(0, 0),
   UniqueBlockByRefTypeID(0), UniqueBlockParmTypeID(0) {
   ObjCIdRedefinitionType = QualType();