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

tools/gn/toolchain.h

Index: tools/gn/toolchain.h
diff --git a/tools/gn/toolchain.h b/tools/gn/toolchain.h
index bcc70c06ee4eb005949ee2a319e9d79b5dd0c0e8..47a3a447842c2812014958cb6ef877eeba173850 100644
--- a/tools/gn/toolchain.h
+++ b/tools/gn/toolchain.h
@@ -44,6 +44,8 @@ class Toolchain : public Item {
     TYPE_LINK,
     TYPE_STAMP,
     TYPE_COPY,
+    TYPE_COPY_BUNDLE_DATA,
+    TYPE_COMPILE_XCASSETS,
 
     TYPE_NUMTYPES  // Must be last.
   };
@@ -60,6 +62,8 @@ class Toolchain : public Item {
   static const char* kToolLink;
   static const char* kToolStamp;
   static const char* kToolCopy;
+  static const char* kToolCopyBundleData;
+  static const char* kToolCompileXCAssets;
 
   Toolchain(const Settings* settings, const Label& label);
   ~Toolchain() override;