Revert "De-couple PredictionMetricsHandler from specific histograms"

This reverts commit 1d11f9fd.

Reason for revert: Suspect for failing test, InputHandlerProxyEventQueueTest.VSyncAlignedGestureScrollPinchScroll
https://ci.chromium.org/p/chromium/builders/ci/Linux%20ChromiumOS%20MSan%20Tests/20826

Original change's description:
> 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/+/2441197
> Reviewed-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}

TBR=sadrul@chromium.org,dtapuska@chromium.org,mabian@microsoft.com

Change-Id: I9cefcdb1b51f13026726eb2449e1213f43dfc91f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1133785
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2451569Reviewed-by: Kristi Park <kristipark@chromium.org>
Commit-Queue: Kristi Park <kristipark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813996}

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

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

ui/base/prediction/prediction_metrics_handler.cc

@@ -2,18 +2,14 @@
 // 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(const char* histogram_name)
-    : histogram_name_(std::move(histogram_name)) {}
-PredictionMetricsHandler::~PredictionMetricsHandler() = default;
+PredictionMetricsHandler::PredictionMetricsHandler() {}
+PredictionMetricsHandler::~PredictionMetricsHandler() {}
 
 void PredictionMetricsHandler::AddRealEvent(const gfx::PointF& pos,
                                             const base::TimeTicks& time_stamp,
@@ -134,25 +130,25 @@ 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(
-        base::StrCat({histogram_name_, ".OverPrediction"}), score);
+    base::UmaHistogramCounts1000(kPredictionMetrics + "OverPrediction", score);
   } else {
-    base::UmaHistogramCounts1000(
-        base::StrCat({histogram_name_, ".UnderPrediction"}), -score);
+    base::UmaHistogramCounts1000(kPredictionMetrics + "UnderPrediction",
+                                 -score);
   }
 
   // Need |last_predicted_| to compute WrongDirection and Jitter metrics.
   if (!last_predicted_.has_value())
     return;
 
-  base::UmaHistogramBoolean(base::StrCat({histogram_name_, ".WrongDirection"}),
+  base::UmaHistogramBoolean(kPredictionMetrics + "WrongDirection",
                             ComputeWrongDirectionMetric());
-  base::UmaHistogramCounts1000(
-      base::StrCat({histogram_name_, ".PredictionJitter"}),
-      ComputePredictionJitterMetric());
-  base::UmaHistogramCounts1000(base::StrCat({histogram_name_, ".VisualJitter"}),
+  base::UmaHistogramCounts1000(kPredictionMetrics + "PredictionJitter",
+                               ComputePredictionJitterMetric());
+  base::UmaHistogramCounts1000(kPredictionMetrics + "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(const char* histogram_name);
+  explicit PredictionMetricsHandler();
   ~PredictionMetricsHandler();
 
   // Struct used to store predicted and real event information.
@@ -103,12 +103,6 @@ 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

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