Tests invalidations produced by scrolling a page with position: fixed elements.

Scroll invalidations[
Exception while running: function onRecordingDone() {
    var event = PerformanceTestRunner.findTimelineEvent(TimelineModel.TimelineModel.RecordType.Paint);
    TestRunner.addArray(
        TimelineModel.InvalidationTracker.invalidationEventsFor(event), PerformanceTestRunner.InvalidationFormatters,
        '', 'Scroll invalidations');
    TestRunner.completeTest();
  }
TypeError: Cannot read property 'length' of null
    at Object.TestRunner.addArray (file:///b/c/b/mac_layout/src/out/Release/resources/inspector/integration_test_runner.js:6003:232)
    at onRecordingDone (evaluateInWebInspector1.js:67:16)
    at result (file:///b/c/b/mac_layout/src/out/Release/resources/inspector/integration_test_runner.js:5943:42)
    at Timeline.TimelinePanel.TestRunner.addSniffer (file:///b/c/b/mac_layout/src/out/Release/resources/inspector/performance_test_runner/performance_test_runner_module.js:5:1190)
    at Timeline.TimelinePanel.result (file:///b/c/b/mac_layout/src/out/Release/resources/inspector/integration_test_runner.js:5943:42)
    at Timeline.TimelinePanel.receiver.(anonymous function) (file:///b/c/b/mac_layout/src/out/Release/resources/inspector/integration_test_runner.js:5937:58)
    at Timeline.TimelineController._finalizeTrace (file:///b/c/b/mac_layout/src/out/Release/resources/inspector/timeline/timeline_module.js:183:99)
    at setTimeout (file:///b/c/b/mac_layout/src/out/Release/resources/inspector/timeline/timeline_module.js:182:76)

