Add a missing include to translation_unit - required after the roll to clang r277962.

tools/clang/translation_unit/TranslationUnitGenerator.cpp

 // Copyright (c) 2014 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.
 //
 // This implements a Clang tool to generate compilation information that is
 // sufficient to recompile the code with clang. For each compilation unit, all
 // source files which are necessary for compiling it are determined. For each
 // compilation unit, a file is created containing a list of all file paths of
 // included files.
 
@@ skipping 13 matching lines @@
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/FrontendActions.h"
 #include "clang/Lex/HeaderSearchOptions.h"
 #include "clang/Lex/PPCallbacks.h"
 #include "clang/Lex/Preprocessor.h"
 #include "clang/Tooling/CommonOptionsParser.h"
 #include "clang/Tooling/CompilationDatabase.h"
 #include "clang/Tooling/Refactoring.h"
 #include "clang/Tooling/Tooling.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Path.h"
 
 using clang::HeaderSearchOptions;
 using clang::tooling::CommonOptionsParser;
 using std::set;
 using std::stack;
 using std::string;
 using std::vector;
 
 namespace {
 // Set of preprocessor callbacks used to record files included.
@@ skipping 219 matching lines @@
   std::unique_ptr<clang::tooling::FrontendActionFactory> frontend_factory =
       clang::tooling::newFrontendActionFactory<CompilationIndexerAction>();
   clang::tooling::ClangTool tool(options.getCompilations(),
                                  options.getSourcePathList());
   // This clang tool does not actually produce edits, but run_tool.py expects
   // this. So we just print an empty edit block.
   llvm::outs() << "==== BEGIN EDITS ====\n";
   llvm::outs() << "==== END EDITS ====\n";
   return tool.run(frontend_factory.get());
 }