[GN] Add support for generating Xcode projects.

tools/gn/commands.h

Index: tools/gn/commands.h
diff --git a/tools/gn/commands.h b/tools/gn/commands.h
index 9d8af5cb7d0d9f4182fd56bd216cd6432a65ef2e..fdd10fcc231a51555c788281664085e8bcdd62cb 100644
--- a/tools/gn/commands.h
+++ b/tools/gn/commands.h
@@ -140,6 +140,12 @@ void FilterTargetsByPatterns(const std::vector<const Target*>& input,
                              const std::vector<LabelPattern>& filter,
                              UniqueVector<const Target*>* output);
 
+// Builds a list of pattern from a semicolon-separated list of labels.
+bool FilterPatternsFromString(const BuildSettings* build_settings,
+                              const std::string& label_list_string,
+                              std::vector<LabelPattern>* filters,
+                              Err* err);
+
 // These are the documentation strings for the command-line flags used by
 // FilterAndPrintTargets. Commands that call that function should incorporate
 // these into their help.