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..49866ce7b05e3c4b88c2ab941bb7a2ae7a480088 100644
--- a/test/file_message_test.dart
+++ b/test/file_message_test.dart
@@ -62,9 +62,7 @@ zip zap zop
   test("works for a point span in an empty file", () {
     expect(new SourceFile("").location(0).pointSpan().message("oh no"),
         equals("""
-line 1, column 1: oh no
-
-^"""));

[Siggi Cherem (dart-lang), 2015/03/21 00:19:59]

would you consider this a breaking change? 

I could preserve the old behavior, but it is nice that if there is no context
(as in the case of an empty file), there is little value for showing this empty
line after all.

[nweiz, 2015/03/24 23:01:17]

No, I don't consider the specific format of [message] to be a guaranteed part of
the API.

[Siggi Cherem (dart-lang), 2015/03/25 00:33:25]

Turns out the fix for this was much easier than I thought, so I decided to keep
this unchanged for the time being.

+line 1, column 1: oh no"""));
   });
 
   test("works for a single-line file without a newline", () {