Store BundleData paths as SourceDirs rather than strings.

tools/gn/bundle_data.cc

 // 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.
 
 #include "tools/gn/bundle_data.h"
 
 #include "base/logging.h"
 #include "tools/gn/filesystem_utils.h"
 #include "tools/gn/output_file.h"
 #include "tools/gn/settings.h"
@@ skipping 87 matching lines @@
   for (const BundleFileRule& file_rule : file_rules_) {
     for (const SourceFile& source : file_rule.sources()) {
       outputs_as_source->push_back(
           file_rule.ApplyPatternToSource(settings, *this, source));
     }
   }
 
   if (!asset_catalog_sources_.empty())
     outputs_as_source->push_back(GetCompiledAssetCatalogPath());
 
-  if (!root_dir_.empty())
+  if (!root_dir_.is_null())
     outputs_as_source->push_back(GetBundleRootDirOutput(settings));
 }
 
 SourceFile BundleData::GetCompiledAssetCatalogPath() const {
   DCHECK(!asset_catalog_sources_.empty());
-  std::string assets_car_path = resources_dir_ + "/Assets.car";
+  std::string assets_car_path = resources_dir_.value() + "/Assets.car";
   return SourceFile(SourceFile::SWAP_IN, &assets_car_path);
 }
 
 SourceFile BundleData::GetBundleRootDirOutput(const Settings* settings) const {
   const SourceDir& build_dir = settings->build_settings()->build_dir();
-  std::string bundle_root_relative = RebasePath(root_dir(), build_dir);
+  std::string bundle_root_relative = RebasePath(root_dir().value(), build_dir);
 
   size_t first_component = bundle_root_relative.find('/');
   if (first_component != std::string::npos) {
     base::StringPiece outermost_bundle_dir =
         base::StringPiece(bundle_root_relative).substr(0, first_component);
     std::string return_value(build_dir.value());
     outermost_bundle_dir.AppendToString(&return_value);
     return SourceFile(SourceFile::SWAP_IN, &return_value);
   }
-  return SourceFile(root_dir());
+  return SourceFile(root_dir().value());
 }