Create pkg/front_end/src/base and begin populating with general use classes.

pkg/front_end/lib/src/base/uri_kind.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.
+
+/**
+ * The enumeration `UriKind` defines the different kinds of URI's that are known to the
+ * analysis engine. These are used to keep track of the kind of URI associated with a given source.
+ */
+class UriKind implements Comparable<UriKind> {
+  /**
+   * A 'dart:' URI.
+   */
+  static const UriKind DART_URI = const UriKind('DART_URI', 0, 0x64);
+
+  /**
+   * A 'file:' URI.
+   */
+  static const UriKind FILE_URI = const UriKind('FILE_URI', 1, 0x66);
+
+  /**
+   * A 'package:' URI.
+   */
+  static const UriKind PACKAGE_URI = const UriKind('PACKAGE_URI', 2, 0x70);
+
+  static const List<UriKind> values = const [DART_URI, FILE_URI, PACKAGE_URI];
+
+  /**
+   * The name of this URI kind.
+   */
+  final String name;
+
+  /**
+   * The ordinal value of the URI kind.
+   */
+  final int ordinal;
+
+  /**
+   * The single character encoding used to identify this kind of URI.
+   */
+  final int encoding;
+
+  /**
+   * Initialize a newly created URI kind to have the given encoding.
+   */
+  const UriKind(this.name, this.ordinal, this.encoding);
+
+  @override
+  int get hashCode => ordinal;
+
+  @override
+  int compareTo(UriKind other) => ordinal - other.ordinal;
+
+  @override
+  String toString() => name;
+
+  /**
+   * Return the URI kind represented by the given [encoding], or `null` if there
+   * is no kind with the given encoding.
+   */
+  static UriKind fromEncoding(int encoding) {
+    while (true) {
+      if (encoding == 0x64) {
+        return DART_URI;
+      } else if (encoding == 0x66) {
+        return FILE_URI;
+      } else if (encoding == 0x70) {
+        return PACKAGE_URI;
+      }
+      break;
+    }
+    return null;
+  }
+
+  /**
+   * Return the URI kind corresponding to the given scheme string.
+   */
+  static UriKind fromScheme(String scheme) {
+    if (scheme == 'package') {
+      return UriKind.PACKAGE_URI;
+    } else if (scheme == 'dart') {
+      return UriKind.DART_URI;
+    } else if (scheme == 'file') {
+      return UriKind.FILE_URI;
+    }
+    return UriKind.FILE_URI;
+  }
+}