Add GN function get_label_info

tools/gn/functions.h

Index: tools/gn/functions.h
diff --git a/tools/gn/functions.h b/tools/gn/functions.h
index d3eb364961a193b82099d4094267ebd5b618188b..6e0aa6db886b7f97c42cff13dc691caf517f112c 100644
--- a/tools/gn/functions.h
+++ b/tools/gn/functions.h
@@ -147,6 +147,14 @@ Value RunGetEnv(Scope* scope,
                 const std::vector<Value>& args,
                 Err* err);
 
+extern const char kGetLabelInfo[];
+extern const char kGetLabelInfo_HelpShort[];
+extern const char kGetLabelInfo_Help[];
+Value RunGetLabelInfo(Scope* scope,
+                      const FunctionCallNode* function,
+                      const std::vector<Value>& args,
+                      Err* err);
+
 extern const char kGetTargetOutputs[];
 extern const char kGetTargetOutputs_HelpShort[];
 extern const char kGetTargetOutputs_Help[];