Replace Rc with Lrc for shared data

src/libsyntax/test_snippet.rs

@@ -13,7 +13,7 @@ use errors::Handler;
 use errors::emitter::EmitterWriter;
 use std::io;
 use std::io::prelude::*;
-use std::rc::Rc;
+use rustc_data_structures::sync::Lrc;
 use std::str;
 use std::sync::{Arc, Mutex};
 use std::path::Path;
@@ -48,7 +48,7 @@ impl<T: Write> Write for Shared<T> {
 fn test_harness(file_text: &str, span_labels: Vec<SpanLabel>, expected_output: &str) {
     let output = Arc::new(Mutex::new(Vec::new()));
 
-    let code_map = Rc::new(CodeMap::new(FilePathMapping::empty()));
+    let code_map = Lrc::new(CodeMap::new(FilePathMapping::empty()));
     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);