add assertions on existing tests with missing doc source

Author: mockersf

src/test/rustdoc/extern-default-method.rs

@@ -4,4 +4,6 @@
 extern crate rustdoc_extern_default_method as ext;
 
 // @count extern_default_method/struct.Struct.html '//*[@id="method.provided"]' 1
+// @has extern_default_method/struct.Struct.html '//div[@id="method.provided"]//a[@class="fnname"]/@href' #method.provided
+// @has extern_default_method/struct.Struct.html '//div[@id="method.provided"]//a[@class="anchor"]/@href' #method.provided
 pub use ext::Struct;