Add TimeToScrollUpdateSwapBegin2 in RAPPOR

content/browser/renderer_host/input/render_widget_host_latency_tracker.cc

Index: content/browser/renderer_host/input/render_widget_host_latency_tracker.cc
diff --git a/content/browser/renderer_host/input/render_widget_host_latency_tracker.cc b/content/browser/renderer_host/input/render_widget_host_latency_tracker.cc
index 3d8de093dfb1a32362ef5bc0182aa0073344d8fa..4248999f60bd105c0e1f8249c3c2de3ae6b4a019 100644
--- a/content/browser/renderer_host/input/render_widget_host_latency_tracker.cc
+++ b/content/browser/renderer_host/input/render_widget_host_latency_tracker.cc
@@ -9,7 +9,10 @@
 #include "base/logging.h"
 #include "base/metrics/histogram_macros.h"
 #include "build/build_config.h"
+#include "components/rappor/public/rappor_utils.h"
 #include "content/browser/renderer_host/render_widget_host_impl.h"
+#include "content/public/browser/content_browser_client.h"
+#include "content/public/common/content_client.h"
 #include "ui/events/blink/web_input_event_traits.h"
 
 using blink::WebGestureEvent;
@@ -238,6 +241,7 @@ void ComputeScrollLatencyHistograms(
 }
 
 void ComputeTouchAndWheelScrollLatencyHistograms(
+    RenderWidgetHostImpl* render_widget_host_impl,
     const ui::LatencyInfo::LatencyComponent& gpu_swap_begin_component,
     const ui::LatencyInfo::LatencyComponent& gpu_swap_end_component,
     int64_t latency_component_id,
@@ -279,6 +283,23 @@ void ComputeTouchAndWheelScrollLatencyHistograms(
           "Event.Latency.ScrollUpdate." + event_type_name +
               ".TimeToScrollUpdateSwapBegin2",
           original_component, gpu_swap_begin_component);
+
+      rappor::RapporService* rappor_service =
+          GetContentClient()->browser()->GetRapporService();
+      if (!rappor_service || !render_widget_host_impl->delegate())
+        return;
+      std::unique_ptr<rappor::Sample> sample =
+          rappor_service->CreateSample(rappor::UMA_RAPPOR_TYPE);
+      render_widget_host_impl->delegate()->AddDomainInfoToRapporSample(
+          sample.get());
+      sample->SetUInt64Field("Latency",
+                             (gpu_swap_begin_component.last_event_time -
+                              original_component.first_event_time)
+                                 .InMicroseconds(),
+                             rappor::NO_NOISE);

[ncarter (slow), 2016/12/08 17:57:27]

Regarding testing, the simplest thing to do would be a unittest that calls this
function directly (you'd have to make it private static in RWHLatencyTracker w/
a test friend), since it's pretty well parameterized. If your test derives from
RenderViewHostImplTestHarness you'll have a WebContents available from the test
fixture, which you can set the URL of and obtain a RWHImpl from.

For testing the rappor side effects, you can create a version of
TestContentBrowserClient that provides a mock implementation of RapporService. A
unittest can install its own content browser client using the pattern here:
https://cs.chromium.org/chromium/src/content/browser/renderer_host/render_vie...

The UMA side effects can be tested via base/histogram_tester.h

+      rappor_service->RecordSample(
+          "Event.Latency.ScrollUpdate.Touch.TimeToScrollUpdateSwapBegin2",

[tdresser, 2016/12/08 18:00:17]

Should we add Event.Latency.ScrollBegin.Touch.TimeToScrollUpdateSwapBegin2 at
the same time?

[Navid Zolghadr, 2016/12/09 19:13:28]

Let me work on adding that and some refactoring between the multiple metrics in
another CL. I just didn't want to make this first metric patch unnecessarily
big.

+          std::move(sample));
     }
   } else {
     // No original component found.
@@ -366,13 +387,15 @@ void AddLatencyInfoComponentIds(LatencyInfo* latency,
 
 }  // namespace
 
-RenderWidgetHostLatencyTracker::RenderWidgetHostLatencyTracker()
+RenderWidgetHostLatencyTracker::RenderWidgetHostLatencyTracker(
+    RenderWidgetHostImpl* render_widget_host_impl)
     : last_event_id_(0),
       latency_component_id_(0),
       device_scale_factor_(1),
       has_seen_first_gesture_scroll_update_(false),
       multi_finger_gesture_(false),
-      touch_start_default_prevented_(false) {}
+      touch_start_default_prevented_(false),
+      render_widget_host_impl(render_widget_host_impl) {}
 
 RenderWidgetHostLatencyTracker::~RenderWidgetHostLatencyTracker() {}
 
@@ -711,8 +734,8 @@ void RenderWidgetHostLatencyTracker::OnFrameSwapped(
   if (source_event_type == ui::SourceEventType::WHEEL ||
       source_event_type == ui::SourceEventType::TOUCH) {
     ComputeTouchAndWheelScrollLatencyHistograms(
-        gpu_swap_begin_component, gpu_swap_end_component, latency_component_id_,
-        latency,
+        render_widget_host_impl, gpu_swap_begin_component,
+        gpu_swap_end_component, latency_component_id_, latency,
         source_event_type == ui::SourceEventType::WHEEL ? "Wheel" : "Touch");
   }