Store BundleData paths as SourceDirs rather than strings.

tools/gn/create_bundle_target_generator.h

 // Copyright 2016 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_CREATE_BUNDLE_TARGET_GENERATOR_H_
 #define TOOLS_GN_CREATE_BUNDLE_TARGET_GENERATOR_H_
 
 #include "base/macros.h"
 #include "tools/gn/target_generator.h"
 
+class SourceDir;
+
 // Populates a Target with the values from a create_bundle rule.
 class CreateBundleTargetGenerator : public TargetGenerator {
  public:
   CreateBundleTargetGenerator(Target* target,
                               Scope* scope,
                               const FunctionCallNode* function_call,
                               Err* err);
   ~CreateBundleTargetGenerator() override;
 
  protected:
   void DoRun() override;
 
  private:
-  bool GetBundleDir(const std::string& bundle_root_dir,
+  bool GetBundleDir(const SourceDir& bundle_root_dir,
                     const base::StringPiece& name,
-                    std::string* bundle_dir);
+                    SourceDir* bundle_dir);
 
   DISALLOW_COPY_AND_ASSIGN(CreateBundleTargetGenerator);
 };
 
 #endif  // TOOLS_GN_CREATE_BUNDLE_TARGET_GENERATOR_H_