Add "bundle_data" target as first step for adding bundle support to gn.

tools/gn/bundle_data_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_BUNDLE_DATA_TARGET_GENERATOR_H_
+#define TOOLS_GN_BUNDLE_DATA_TARGET_GENERATOR_H_
+
+#include "base/macros.h"
+#include "tools/gn/target_generator.h"
+
+// Populates a Target with the values from a bundle_data rule.
+class BundleDataTargetGenerator : public TargetGenerator {
+ public:
+  BundleDataTargetGenerator(Target* target,
+                            Scope* scope,
+                            const FunctionCallNode* function_call,
+                            Err* err);
+  ~BundleDataTargetGenerator() override;
+
+ protected:
+  void DoRun() override;
+
+ private:
+  bool FillOutputs();
+
+  bool EnsureSubstitutionIsInBundleDir(
+      const SubstitutionPattern& pattern,
+      const Value& original_value);
+
+  DISALLOW_COPY_AND_ASSIGN(BundleDataTargetGenerator);
+};
+
+#endif  // TOOLS_GN_BUNDLE_DATA_TARGET_GENERATOR_H_