Introduce span with line context

test/file_message_test.dart

Index: test/file_message_test.dart
diff --git a/test/file_message_test.dart b/test/file_message_test.dart
index 18b34e71bc276f44edd9e053a0e9000133e2eced..cbda09aacf265be8fdde5a342e588d272fbab070 100644
--- a/test/file_message_test.dart
+++ b/test/file_message_test.dart
@@ -60,16 +60,15 @@ zip zap zop
   });
 
   test("works for a point span in an empty file", () {
-    expect(new SourceFile("").location(0).pointSpan().message("oh no"),
-        equals("""
+    expect(new SourceFile("").location(0).pointSpan().message("oh no"), equals(
+        """
 line 1, column 1: oh no
 
 ^"""));
   });
 
   test("works for a single-line file without a newline", () {
-    expect(new SourceFile("foo bar").span(0, 7).message("oh no"),
-        equals("""
+    expect(new SourceFile("foo bar").span(0, 7).message("oh no"), equals("""
 line 1, column 1: oh no
 foo bar
 ^^^^^^^"""));