Add dummy dart:html library for documentation.

lib/html/doc/interface/PerformanceTiming.dartdoc

Index: lib/html/doc/interface/PerformanceTiming.dartdoc
diff --git a/lib/html/doc/interface/PerformanceTiming.dartdoc b/lib/html/doc/interface/PerformanceTiming.dartdoc
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+// Copyright (c) 2012, 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.
+
+// WARNING:
+//   This file contains documentation that is merged into the real source.
+//   Do not make code changes here.
+
+/// @domName PerformanceTiming
+interface PerformanceTiming {
+
+  /** @domName PerformanceTiming.connectEnd */
+  final int connectEnd;
+
+  /** @domName PerformanceTiming.connectStart */
+  final int connectStart;
+
+  /** @domName PerformanceTiming.domComplete */
+  final int domComplete;
+
+  /** @domName PerformanceTiming.domContentLoadedEventEnd */
+  final int domContentLoadedEventEnd;
+
+  /** @domName PerformanceTiming.domContentLoadedEventStart */
+  final int domContentLoadedEventStart;
+
+  /** @domName PerformanceTiming.domInteractive */
+  final int domInteractive;
+
+  /** @domName PerformanceTiming.domLoading */
+  final int domLoading;
+
+  /** @domName PerformanceTiming.domainLookupEnd */
+  final int domainLookupEnd;
+
+  /** @domName PerformanceTiming.domainLookupStart */
+  final int domainLookupStart;
+
+  /** @domName PerformanceTiming.fetchStart */
+  final int fetchStart;
+
+  /** @domName PerformanceTiming.loadEventEnd */
+  final int loadEventEnd;
+
+  /** @domName PerformanceTiming.loadEventStart */
+  final int loadEventStart;
+
+  /** @domName PerformanceTiming.navigationStart */
+  final int navigationStart;
+
+  /** @domName PerformanceTiming.redirectEnd */
+  final int redirectEnd;
+
+  /** @domName PerformanceTiming.redirectStart */
+  final int redirectStart;
+
+  /** @domName PerformanceTiming.requestStart */
+  final int requestStart;
+
+  /** @domName PerformanceTiming.responseEnd */
+  final int responseEnd;
+
+  /** @domName PerformanceTiming.responseStart */
+  final int responseStart;
+
+  /** @domName PerformanceTiming.secureConnectionStart */
+  final int secureConnectionStart;
+
+  /** @domName PerformanceTiming.unloadEventEnd */
+  final int unloadEventEnd;
+
+  /** @domName PerformanceTiming.unloadEventStart */
+  final int unloadEventStart;
+}