Write a phony target for the top-level directory of a create_bundle target.

tools/gn/bundle_data.h

Index: tools/gn/bundle_data.h
diff --git a/tools/gn/bundle_data.h b/tools/gn/bundle_data.h
index e78589e9e91cfce01f68a10928cafe92732965e9..aaf5e3362d3a9b75004c99004575fb4ad14a08f8 100644
--- a/tools/gn/bundle_data.h
+++ b/tools/gn/bundle_data.h
@@ -64,6 +64,18 @@ class BundleData {
   // asset_catalog_sources() is not empty.
   SourceFile GetCompiledAssetCatalogPath() const;
 
+  // Returns the path to the top-level directory of the bundle. This is
+  // based on root_dir(), but since that can be Bundle.app/Contents/ or
+  // any other subpath, this is just the most top-level directory (e.g.,
+  // just Bundle.app/).
+  //
+  // Note that this is a SourceFile instead of a SourceDir. This is because
+  // the output of a create_bundle rule is a single logical unit, even though
+  // it is really a directory containing many outputs. This allows other
+  // targets to treat the bundle as a single unit, rather than a collection
+  // of its contents.
+  SourceFile GetBundleRootDirOutput(const Settings* settings) const;
+
   // Returns the list of inputs for the compilation of the asset catalog.
   SourceFiles& asset_catalog_sources() { return asset_catalog_sources_; }
   const SourceFiles& asset_catalog_sources() const {