Inline char_at() and record_width.

Because `bump()` is hot.

src/libsyntax/str.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[inline]
 pub fn char_at(s: &str, byte: usize) -> char {
     s[byte..].chars().next().unwrap()
 }

src/libsyntax_pos/lib.rs

@@ -1047,6 +1047,7 @@ impl FileMap {
         self.multibyte_chars.borrow_mut().push(mbc);
     }
 
+    #[inline]
     pub fn record_width(&self, pos: BytePos, ch: char) {
         let width = match ch {
             '\t' =>