Replace RE2 import with a dependency

third_party/re2/re2/testing/null_walker.cc

-// Copyright 2009 The RE2 Authors.  All Rights Reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-#include "util/test.h"
-#include "re2/regexp.h"
-#include "re2/walker-inl.h"
-
-namespace re2 {
-
-// Null walker.  For benchmarking the walker itself.
-
-class NullWalker : public Regexp::Walker<bool> {
- public:
-  NullWalker() { }
-  bool PostVisit(Regexp* re, bool parent_arg, bool pre_arg,
-                 bool* child_args, int nchild_args);
-
-  bool ShortVisit(Regexp* re, bool a) {
-    // Should never be called: we use Walk not WalkExponential.
-    LOG(DFATAL) << "NullWalker::ShortVisit called";
-    return a;
-  }
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(NullWalker);
-};
-
-// Called after visiting re's children.  child_args contains the return
-// value from each of the children's PostVisits (i.e., whether each child
-// can match an empty string).  Returns whether this clause can match an
-// empty string.
-bool NullWalker::PostVisit(Regexp* re, bool parent_arg, bool pre_arg,
-                                  bool* child_args, int nchild_args) {
-  return false;
-}
-
-// Returns whether re can match an empty string.
-void Regexp::NullWalk() {
-  NullWalker w;
-  w.Walk(this, false);
-}
-
-}  // namespace re2