Add a sampling scheme to ScrollUpdate.Touch UKM

content/browser/renderer_host/input/render_widget_host_latency_tracker_unittest.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/input/render_widget_host_latency_tracker.h"
 #include "base/metrics/metrics_hashes.h"
 #include "base/test/histogram_tester.h"
 #include "components/metrics/proto/ukm/entry.pb.h"
 #include "components/rappor/public/rappor_utils.h"
 #include "components/rappor/test_rappor_service.h"
@@ skipping 79 matching lines @@
 
  private:
   rappor::TestRapporServiceImpl rappor_service_;
   ukm::TestUkmRecorder test_ukm_recorder_;
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostLatencyTrackerTestBrowserClient);
 };
 
 class RenderWidgetHostLatencyTrackerTest
     : public RenderViewHostImplTestHarness {
  public:
-  RenderWidgetHostLatencyTrackerTest() : old_browser_client_(NULL) {
+  RenderWidgetHostLatencyTrackerTest()
+      : tracker_(false), old_browser_client_(NULL) {
     tracker_.Initialize(kTestRoutingId, kTestProcessId);
     ResetHistograms();
   }
 
   ::testing::AssertionResult RapporSampleAssert(const char* rappor_name,
                                                 int count) {
     rappor::TestSample::Shadow* sample_obj =
         test_browser_client_.getTestRapporService()->GetRecordedSampleForMetric(
             rappor_name);
     if (count) {
@@ skipping 1276 matching lines @@
           "QueueingDurationWhenExpectedQueueingTime_GreaterThan.300ms"),
       ElementsAre(Bucket(event_timestamps_ms[1] - event_timestamps_ms[0], 1)));
 
   EXPECT_THAT(histogram_tester().GetAllSamples(
                   "RendererScheduler."
                   "QueueingDurationWhenExpectedQueueingTime_GreaterThan.450ms"),
               ElementsAre());
 }
 
 }  // namespace content