add h2 pushed requests artifact

lighthouse-core/gather/computed/pushed-requests.js

@@ -0,0 +1,46 @@
+/**
+ * @license
+ * Copyright 2016 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+'use strict';
+
+const ComputedArtifact = require('./computed-artifact');
+
+class PushedRequests extends ComputedArtifact {
+
+  get name() {
+    return 'PushedRequests';
+  }
+
+  filterPushed(records) {
+    const pushedRecords = records.filter(r => r._timing && !!r._timing.pushStart);
+    return Promise.resolve(pushedRecords);
+  }
+
+  request(networkRecords) {
+    if (this.cache.has(networkRecords)) {
+      return this.cache.get(networkRecords);
+    }
+
+    return this.filterPushed(networkRecords).then(records => {
+      this.cache.set(records, networkRecords);
+      return records;
+    });
+  }
+
+}
+
+module.exports = PushedRequests;