Use PathBuf instead of String where applicable

src/libsyntax/test_snippet.rs

@@ -16,6 +16,7 @@ use std::io::prelude::*;
 use std::rc::Rc;
 use std::str;
 use std::sync::{Arc, Mutex};
+use std::path::Path;
 use syntax_pos::{BytePos, NO_EXPANSION, Span, MultiSpan};
 
 /// Identify a position in the text by the Nth occurrence of a string.
@@ -48,7 +49,7 @@ fn test_harness(file_text: &str, span_labels: Vec<SpanLabel>, expected_output: &
     let output = Arc::new(Mutex::new(Vec::new()));
 
     let code_map = Rc::new(CodeMap::new(FilePathMapping::empty()));
-    code_map.new_filemap_and_lines("test.rs", &file_text);
+    code_map.new_filemap_and_lines(Path::new("test.rs"), &file_text);
 
     let primary_span = make_span(&file_text, &span_labels[0].start, &span_labels[0].end);
     let mut msp = MultiSpan::from_span(primary_span);