Added missing impl_to_source! and impl_to_tokens! for ImplItem.

This fixes several use cases that were broken after #23265 landed.

src/libsyntax/ext/quote.rs

@@ -176,6 +176,7 @@ pub mod rt {
     impl_to_source! { ast::Arg, arg_to_string }
     impl_to_source! { Generics, generics_to_string }
     impl_to_source! { P<ast::Item>, item_to_string }
+    impl_to_source! { P<ast::ImplItem>, impl_item_to_string }
     impl_to_source! { P<ast::Stmt>, stmt_to_string }
     impl_to_source! { P<ast::Expr>, expr_to_string }
     impl_to_source! { P<ast::Pat>, pat_to_string }
@@ -308,6 +309,7 @@ pub mod rt {
 
     impl_to_tokens! { ast::Ident }
     impl_to_tokens! { P<ast::Item> }
+    impl_to_tokens! { P<ast::ImplItem> }
     impl_to_tokens! { P<ast::Pat> }
     impl_to_tokens! { ast::Arm }
     impl_to_tokens_lifetime! { &'a [P<ast::Item>] }

src/libsyntax/print/pprust.rs

@@ -355,6 +355,10 @@ pub fn item_to_string(i: &ast::Item) -> String {
     $to_string(|s| s.print_item(i))
 }
 
+pub fn impl_item_to_string(i: &ast::ImplItem) -> String {
+    $to_string(|s| s.print_impl_item(i))
+}
+
 pub fn generics_to_string(generics: &ast::Generics) -> String {
     $to_string(|s| s.print_generics(generics))
 }