Add TimeToScrollUpdateSwapBegin2 to UKM

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 26f0c1e5e751e92686dbf821056e85c8df926dc2..9b1e1db6c2d12a34d745cb393d52c34b176b9daa 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
@@ -11,6 +11,8 @@
 #include "base/metrics/histogram_macros.h"
 #include "build/build_config.h"
 #include "components/rappor/public/rappor_utils.h"
+#include "components/ukm/public/ukm_entry_builder.h"
+#include "components/ukm/public/ukm_recorder.h"
 #include "content/browser/renderer_host/render_widget_host_delegate.h"
 #include "content/public/browser/content_browser_client.h"
 #include "content/public/common/content_client.h"
@@ -27,6 +29,8 @@ using ui::LatencyInfo;
 namespace content {
 namespace {
 
+const char kLatency[] = "Latency";
+
 std::string WebInputEventTypeToInputModalityString(WebInputEvent::Type type) {
   if (type == blink::WebInputEvent::kMouseWheel) {
     return "Wheel";
@@ -325,4 +329,35 @@ void RenderWidgetHostLatencyTracker::ReportRapporScrollLatency(
   }
 }
 
+int32_t RenderWidgetHostLatencyTracker::GetUkmSourceId() {

[tdresser, 2017/05/30 16:52:07]

The name of this implies to me that it always gets the same id, but it looks
like it actually gets a new id each time.

Which is correct?

[Navid Zolghadr, 2017/05/31 20:37:15]

I wasn't sure if I had to reuse the id. But now that I look again at other
samples they do use the same id.

+  ukm::UkmRecorder* ukm_recorder =
+      GetContentClient()->browser()->GetUkmRecorder();

[Navid Zolghadr, 2017/05/26 15:15:43]

I recently added this plumbing in this CL:
https://codereview.chromium.org/2877673003/

But at the same time there was another change exposing a static function
ukm::UkmRecorder::Get()
https://cs.chromium.org/chromium/src/components/ukm/public/ukm_recorder.cc?ty...

to get the UkmRecorder. So the question I have is which one to use? Is the
plumbing I added is alright or is it better to just use ukm::UkmRecorder::Get()
instead to get the UkmRecorder and remove my plumbing?
Also do I need to do anything special to get the UkmRecorder instance created
for this process (as per comment above ukm::UkmRecorder::Get())

[rkaplow, 2017/05/30 20:03:32]

+oystein - can you answer

[Navid Zolghadr, 2017/05/31 20:37:15]

I started using ukm::UkmRecorder::Get() and removed my own plumbing.

+  int32_t ukm_source_id = -1;
+  if (ukm_recorder) {
+    ukm_source_id = ukm_recorder->GetNewSourceID();
+    render_widget_host_delegate_->UpdateUrlForUkmSource(ukm_recorder,
+                                                        ukm_source_id);
+  }
+  return ukm_source_id;
+}
+
+void RenderWidgetHostLatencyTracker::ReportUkmScrollLatency(
+    const std::string& name,
+    const LatencyInfo::LatencyComponent& start_component,
+    const LatencyInfo::LatencyComponent& end_component) {
+  CONFIRM_VALID_TIMING(start_component, end_component)
+
+  int32_t ukm_source_id = GetUkmSourceId();
+  if (ukm_source_id == -1)
+    return;
+
+  ukm::UkmRecorder* ukm_recorder =
+      GetContentClient()->browser()->GetUkmRecorder();
+
+  std::unique_ptr<ukm::UkmEntryBuilder> builder =

[tdresser, 2017/05/30 16:52:07]

Does this need to be a unique_ptr, or can it be stack allocated?

[Navid Zolghadr, 2017/05/31 20:37:15]

You mean the normal object with no pointer? But the GetEntryBuilder returns a
pointer. The usage instructions are here:
https://cs.chromium.org/chromium/src/components/ukm/public/mojo_ukm_recorder....

[tdresser, 2017/06/01 12:44:44]

Acknowledged.

+      ukm_recorder->GetEntryBuilder(ukm_source_id, name.c_str());
+  builder->AddMetric(kLatency, (end_component.last_event_time -
+                                start_component.first_event_time)
+                                   .InMicroseconds());
+}
 }  // namespace content