Add test for expected source mappings

tests/compiler/dart2js/sourcemaps/stacktrace_test.dart

Index: tests/compiler/dart2js/sourcemaps/stacktrace_test.dart
diff --git a/tests/compiler/dart2js/sourcemaps/stacktrace_test.dart b/tests/compiler/dart2js/sourcemaps/stacktrace_test.dart
index 2a4589ba1ac8a417e6e732b2999ca1c7b8ea5c82..6bd7621b47c6f648d3933424d7833558a4e1a58f 100644
--- a/tests/compiler/dart2js/sourcemaps/stacktrace_test.dart
+++ b/tests/compiler/dart2js/sourcemaps/stacktrace_test.dart
@@ -209,14 +209,10 @@ class Test {
   Test(this.code, this.expectedLines, this.unexpectedLines);
 }
 
-const int _LF = 0x0A;
-const int _CR = 0x0D;
-const int _LBRACE = 0x7B;
-
 Test processTestCode(String code) {
   Map<int, StackTraceLine> stackTraceMap = <int, StackTraceLine>{};
   List<StackTraceLine> unexpectedLines = <StackTraceLine>[];
-  AnnotatedCode annotatedCode = new AnnotatedCode(code);
+  AnnotatedCode annotatedCode = new AnnotatedCode.fromText(code);
   for (Annotation annotation in annotatedCode.annotations) {
     int colonIndex = annotation.text.indexOf(':');
     String indexText = annotation.text.substring(0, colonIndex);