Add test- and group-level support for skipping tests.

lib/src/backend/metadata.dart

 // Copyright (c) 2015, 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 test.backend.metadata;
 
 import '../frontend/timeout.dart';
 import 'platform_selector.dart';
 
 /// Metadata for a test or test suite.
 ///
 /// This metadata comes from declarations on the test itself; it doesn't include
 /// configuration from the user.
 class Metadata {
   /// The selector indicating which platforms the suite supports.
   final PlatformSelector testOn;
 
   /// The modification to the timeout for the test or suite.
   final Timeout timeout;
 
+  /// Whether the test or suite should be skipped.
+  final bool skip;
+
+  /// The reason the test or suite should be skipped, if given.
+  final String skipReason;
+
   /// Creates new Metadata.
   ///
   /// [testOn] defaults to [PlatformSelector.all].
-  Metadata({PlatformSelector testOn, Timeout timeout})
+  Metadata({PlatformSelector testOn, Timeout timeout, bool skip: false,
+          this.skipReason})
       : testOn = testOn == null ? PlatformSelector.all : testOn,
-        timeout = timeout == null ? const Timeout.factor(1) : timeout;
+        timeout = timeout == null ? const Timeout.factor(1) : timeout,
+        skip = skip;
 
   /// Creates a new Metadata, but with fields parsed from strings where
   /// applicable.
   ///
   /// Throws a [FormatException] if any field is invalid.
-  Metadata.parse({String testOn, Timeout timeout})
-      : this(
-          testOn: testOn == null ? null : new PlatformSelector.parse(testOn),
-          timeout: timeout);
+  Metadata.parse({String testOn, Timeout timeout, skip})
+      : testOn = testOn == null
+            ? PlatformSelector.all
+            : new PlatformSelector.parse(testOn),
+        timeout = timeout == null ? const Timeout.factor(1) : timeout,
+        skip = skip != null && skip != false,
+        skipReason = skip is String ? skip : null {
+    if (skip != null && skip is! String && skip is! bool) {
+      throw new ArgumentError(
+          '"skip" must be a String or a bool, was "$skip".');
+    }
+  }
 
   /// Dezerializes the result of [Metadata.serialize] into a new [Metadata].
   Metadata.deserialize(serialized)
       : this.parse(
           testOn: serialized['testOn'],
           timeout: serialized['timeout']['duration'] == null
               ? new Timeout.factor(serialized['timeout']['scaleFactor'])
               : new Timeout(new Duration(
-                  microseconds: serialized['timeout']['duration'])));
+                  microseconds: serialized['timeout']['duration'])),
+          skip: serialized['skipReason'] == null
+              ? serialized['skip']
+              : serialized['skipReason']);
 
   /// Return a new [Metadata] that merges [this] with [other].
   ///
   /// If the two [Metadata]s have conflicting properties, [other] wins.
   Metadata merge(Metadata other) =>
       new Metadata(
           testOn: testOn.intersect(other.testOn),
-          timeout: timeout.merge(other.timeout));
+          timeout: timeout.merge(other.timeout),
+          skip: skip || other.skip,
+          skipReason: other.skipReason == null ? skipReason : other.skipReason);
 
   /// Serializes [this] into a JSON-safe object that can be deserialized using
   /// [new Metadata.deserialize].
   serialize() => {
     'testOn': testOn == PlatformSelector.all ? null : testOn.toString(),
     'timeout': {
       'duration': timeout.duration == null
           ? null
           : timeout.duration.inMicroseconds,
       'scaleFactor': timeout.scaleFactor
-    }
+    },
+    'skip': skip,
+    'skipReason': skipReason
   };
 }