Add inference test functionality based on code point id.

tests/compiler/dart2js/annotated_code_helper.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+const int _LF = 0x0A;
+const int _CR = 0x0D;
+const int _LBRACE = 0x7B;
+
+class Annotation {
+  /// 1-based line number of the annotation.
+  final int lineNo;
+
+  /// 1-based column number of the annotation.
+  final int columnNo;
+
+  /// 0-based character offset with

[Siggi Cherem (dart-lang), 2017/01/24 21:05:59]

with => of the annotation?

[Johnni Winther, 2017/01/25 13:28:13]

Done.

+  final int offset;
+
+  /// The text in the annotation.
+  final String text;
+
+  Annotation(this.lineNo, this.columnNo, this.offset, this.text);
+}
+
+class AnnotatedCode {

[Siggi Cherem (dart-lang), 2017/01/24 21:05:59]

add a short dart doc with an example of the syntax of the annotations

[Johnni Winther, 2017/01/25 13:28:13]

Done.

+  final String sourceCode;

[Siggi Cherem (dart-lang), 2017/01/24 21:05:59]

+ dartdoc or rename to unannotatedCode?

[Johnni Winther, 2017/01/25 13:28:13]

Done.

+  final List<Annotation> annotations;
+
+  AnnotatedCode(this.sourceCode, this.annotations);
+}
+
+AnnotatedCode processAnnotatedCode(String code) {

[Siggi Cherem (dart-lang), 2017/01/24 21:05:59]

optional nit: rename or move as a factory constructor of annotated code? Maybe:

  factory AnnotatedCode.parse(String annotatedCode) { ... }

[Johnni Winther, 2017/01/25 13:28:13]

Done.

+  StringBuffer codeBuffer = new StringBuffer();
+  List<Annotation> annotations = <Annotation>[];
+  int index = 0;
+  int offset = 0;
+  int lineNo = 1;
+  int columnNo = 1;
+  while (index < code.length) {
+    int charCode = code.codeUnitAt(index);
+    switch (charCode) {
+      case _LF:
+        codeBuffer.write('\n');
+        offset++;
+        lineNo++;
+        columnNo = 1;
+        break;
+      case _CR:
+        if (index + 1 < code.length && code.codeUnitAt(index + 1) == _LF) {
+          index++;
+        }
+        codeBuffer.write('\n');
+        offset++;
+        lineNo++;
+        columnNo = 1;
+        break;
+      case 0x40:

[Siggi Cherem (dart-lang), 2017/01/24 21:05:59]

define 0x40 too?

+        if (index + 1 < code.length && code.codeUnitAt(index + 1) == _LBRACE) {
+          int endIndex = code.indexOf('}', index);
+          String text = code.substring(index + 2, endIndex);
+          annotations.add(new Annotation(lineNo, columnNo, offset, text));
+          index = endIndex;
+        } else {
+          codeBuffer.writeCharCode(charCode);
+          offset++;
+          columnNo++;
+        }
+        break;
+      default:
+        codeBuffer.writeCharCode(charCode);
+        offset++;
+        columnNo++;
+    }
+    index++;
+  }
+  return new AnnotatedCode(codeBuffer.toString(), annotations);
+}