Optimize successive calls SourceFile.getLine().

lib/src/location.dart

Index: lib/src/location.dart
diff --git a/lib/src/location.dart b/lib/src/location.dart
index 27057424b1f3cf4ada9b14142654aabc24251c80..42e2b7dd78152a571ffca14321f1c042aed27af5 100644
--- a/lib/src/location.dart
+++ b/lib/src/location.dart
@@ -44,11 +44,11 @@ class SourceLocation implements Comparable<SourceLocation> {
         line = line == null ? 0 : line,
         column = column == null ? offset : column {
     if (this.offset < 0) {
-      throw new RangeError("Offset may not be negative, was $offset.");
+      throw new RangeError("Offset may not be negative, was ${this.offset}.");
     } else if (this.line < 0) {
-      throw new RangeError("Line may not be negative, was $line.");
+      throw new RangeError("Line may not be negative, was ${this.line}.");
     } else if (this.column < 0) {
-      throw new RangeError("Column may not be negative, was $column.");
+      throw new RangeError("Column may not be negative, was ${this.column}.");
     }
   }