De-couple PredictionMetricsHandler from specific histograms

PredictionMetricsHandler appears to be designed to work for anything
that is predicting points. However, it currently only reports metrics
in the Event.InputEventPrediction.Scroll* histograms. De-couple the
class from these histograms so it can be used for things only than
scroll metrics.

Bug: 1133785
Change-Id: Ib34129fc46b20b45810cbd5ca195483e88c513e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2441197Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Mario Bianucci <mabian@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#813813}

third_party/blink/renderer/platform/widget/input/scroll_predictor.cc

@@ -13,7 +13,8 @@
 
 namespace blink {
 
-ScrollPredictor::ScrollPredictor() {
+ScrollPredictor::ScrollPredictor()
+    : metrics_handler_("Event.InputEventPrediction.Scroll") {
   // Get the predictor from feature flags
   std::string predictor_name = GetFieldTrialParamValueByFeature(
       blink::features::kResamplingScrollEvents, "predictor");

ui/base/prediction/prediction_metrics_handler.cc

@@ -2,14 +2,18 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <utility>
+
 #include "ui/base/prediction/prediction_metrics_handler.h"
 
 #include "base/metrics/histogram_functions.h"
+#include "base/strings/strcat.h"
 
 namespace ui {
 
-PredictionMetricsHandler::PredictionMetricsHandler() {}
-PredictionMetricsHandler::~PredictionMetricsHandler() {}
+PredictionMetricsHandler::PredictionMetricsHandler(const char* histogram_name)
+    : histogram_name_(std::move(histogram_name)) {}
+PredictionMetricsHandler::~PredictionMetricsHandler() = default;
 
 void PredictionMetricsHandler::AddRealEvent(const gfx::PointF& pos,
                                             const base::TimeTicks& time_stamp,
@@ -130,25 +134,25 @@ void PredictionMetricsHandler::ComputeMetrics() {
   for (int i = 0; i < first_needed_event - 1; i++)
     events_queue_.pop_front();
 
-  std::string kPredictionMetrics = "Event.InputEventPrediction.Scroll.";
-
   double score = ComputeOverUnderPredictionMetric();
   if (score >= 0) {
-    base::UmaHistogramCounts1000(kPredictionMetrics + "OverPrediction", score);
+    base::UmaHistogramCounts1000(
+        base::StrCat({histogram_name_, ".OverPrediction"}), score);
   } else {
-    base::UmaHistogramCounts1000(kPredictionMetrics + "UnderPrediction",
-                                 -score);
+    base::UmaHistogramCounts1000(
+        base::StrCat({histogram_name_, ".UnderPrediction"}), -score);
   }
 
   // Need |last_predicted_| to compute WrongDirection and Jitter metrics.
   if (!last_predicted_.has_value())
     return;
 
-  base::UmaHistogramBoolean(kPredictionMetrics + "WrongDirection",
+  base::UmaHistogramBoolean(base::StrCat({histogram_name_, ".WrongDirection"}),
                             ComputeWrongDirectionMetric());
-  base::UmaHistogramCounts1000(kPredictionMetrics + "PredictionJitter",
-                               ComputePredictionJitterMetric());
-  base::UmaHistogramCounts1000(kPredictionMetrics + "VisualJitter",
+  base::UmaHistogramCounts1000(
+      base::StrCat({histogram_name_, ".PredictionJitter"}),
+      ComputePredictionJitterMetric());
+  base::UmaHistogramCounts1000(base::StrCat({histogram_name_, ".VisualJitter"}),
                                ComputeVisualJitterMetric());
 }
 

ui/base/prediction/prediction_metrics_handler.h

@@ -25,7 +25,7 @@ class PredictionMetricsHandlerTest;
 // few metrics.
 class COMPONENT_EXPORT(UI_BASE_PREDICTION) PredictionMetricsHandler {
  public:
-  explicit PredictionMetricsHandler();
+  explicit PredictionMetricsHandler(const char* histogram_name);
   ~PredictionMetricsHandler();
 
   // Struct used to store predicted and real event information.
@@ -103,6 +103,12 @@ class COMPONENT_EXPORT(UI_BASE_PREDICTION) PredictionMetricsHandler {
   base::Optional<gfx::PointF> last_predicted_ = base::nullopt;
   // The first real event position which time is later than the predicted time.
   gfx::PointF next_real_;
+
+  // Beginning of the full histogram name. It will have the various metrics'
+  // names (.OverPrediction, .UnderPrediction, .WrongDirection,
+  // .PredictionJitter, .VisualJitter) appended to it when counting the metric
+  // in a histogram.
+  const char* const histogram_name_;
 };
 
 }  // namespace ui

ui/base/prediction/prediction_metrics_handler_unittest.cc

@@ -29,7 +29,8 @@ class PredictionMetricsHandlerTest : public testing::Test {
   explicit PredictionMetricsHandlerTest() {}
 
   void SetUp() override {
-    metrics_handler_ = std::make_unique<PredictionMetricsHandler>();
+    metrics_handler_ = std::make_unique<PredictionMetricsHandler>(
+        "Event.InputEventPrediction.Scroll");
     histogram_tester_ = std::make_unique<base::HistogramTester>();
   }