Add "create_bundle" target in order to support bundle with gn.

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"
+
+// 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,
+                    const base::StringPiece& name,
+                    std::string* bundle_dir);
+
+  DISALLOW_COPY_AND_ASSIGN(CreateBundleTargetGenerator);
+};
+
+#endif  // TOOLS_GN_CREATE_BUNDLE_TARGET_GENERATOR_H_