Add a UniqueVector class to GN

tools/gn/source_dir.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef TOOLS_GN_SOURCE_DIR_H_
 #define TOOLS_GN_SOURCE_DIR_H_
 
+#include <algorithm>
 #include <string>
 
 #include "base/containers/hash_tables.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/strings/string_piece.h"
 
 class SourceFile;
 
 // Represents a directory within the source tree. Source dirs begin and end in
@@ skipping 65 matching lines @@
   bool operator==(const SourceDir& other) const {
     return value_ == other.value_;
   }
   bool operator!=(const SourceDir& other) const {
     return !operator==(other);
   }
   bool operator<(const SourceDir& other) const {
     return value_ < other.value_;
   }
 
+  void swap(SourceDir& other) {
+    value_.swap(other.value_);
+  }
+
  private:
   friend class SourceFile;
   std::string value_;
 
   // Copy & assign supported.
 };
 
 namespace BASE_HASH_NAMESPACE {
 
 #if defined(COMPILER_GCC)
 template<> struct hash<SourceDir> {
   std::size_t operator()(const SourceDir& v) const {
     hash<std::string> h;
     return h(v.value());
   }
 };
 #elif defined(COMPILER_MSVC)
 inline size_t hash_value(const SourceDir& v) {
   return hash_value(v.value());
 }
 #endif  // COMPILER...
 
 }  // namespace BASE_HASH_NAMESPACE
 
+inline void swap(SourceDir& lhs, SourceDir& rhs) {
+  lhs.swap(rhs);
+}
+
 #endif  // TOOLS_GN_SOURCE_DIR_H_