Add GN function get_label_info

tools/gn/settings.h

Index: tools/gn/settings.h
diff --git a/tools/gn/settings.h b/tools/gn/settings.h
index f2e8925fdfc21e2c3911d68e4bf9560b69a8ef6e..e66a13f6a35736bfd2383766e8dc5259391318b1 100644
--- a/tools/gn/settings.h
+++ b/tools/gn/settings.h
@@ -33,10 +33,12 @@ class Settings {
     WIN
   };
 
-  // Constructs a toolchain settings. The output_subdir_name is the name we
-  // should use for the subdirectory in the build output directory for this
-  // toolchain's outputs. It should have no slashes in it. The default
-  // toolchain should use an empty string.
+  // Constructs a toolchain settings.
+  //
+  // The output_subdir_name is the name we should use for the subdirectory in
+  // the build output directory for this toolchain's outputs. The default
+  // toolchain would use an empty string (it goes in the root build dir).
+  // Otherwise, it must end in a slash.
   Settings(const BuildSettings* build_settings,
            const std::string& output_subdir_name);
   ~Settings();