Move scanner into pkg/front_end/lib/src/scanner.

pkg/front_end/lib/src/scanner/string_utilities.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.
+
+library front_end.src.scanner.string_utilities;
+
+import 'package:front_end/src/scanner/interner.dart';
+
+class StringUtilities {
+  static Interner INTERNER = new NullInterner();
+
+  static bool endsWith3(String str, int c1, int c2, int c3) {

[Brian Wilkerson, 2016/11/08 20:53:24]

We might want to verify that these methods are still more performant than
String.endsWith and String.startsWith before pulling them over.

+    var length = str.length;
+    return length >= 3 &&
+        str.codeUnitAt(length - 3) == c1 &&
+        str.codeUnitAt(length - 2) == c2 &&
+        str.codeUnitAt(length - 1) == c3;
+  }
+
+  static String intern(String string) => INTERNER.intern(string);
+
+  static bool startsWith3(String str, int start, int c1, int c2, int c3) {
+    return str.length - start >= 3 &&
+        str.codeUnitAt(start) == c1 &&
+        str.codeUnitAt(start + 1) == c2 &&
+        str.codeUnitAt(start + 2) == c3;
+  }
+}