Clean up in analytics

This
- converts PercentileCalculator to sort entries, as previously suggested,
- adds the number of values to the dump of a PercentileCalculator, and
- fixes the name of a class to conform to conventions.

Change-Id: Icb25a3adfc922b6d5b394883853eeeff968e4b89
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/245460
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

Author: bwilkerson

pkg/analysis_server/lib/src/analytics/percentile_calculator.dart

@@ -35,16 +35,17 @@ class PercentileCalculator {
       return 0;
     }
     var targetIndex = _valueCount * percentile / 100;
-    var values = _counts.keys.toList()..sort();
+    var entries = _counts.entries.toList()
+      ..sort((first, second) => first.key.compareTo(second.key));
     // The number of values represented by walking the counts.
     var accumulation = 0;
-    for (var i = 0; i < values.length; i++) {
-      var value = values[i];
-      accumulation += _counts[value]!;
+    for (var i = 0; i < entries.length; i++) {
+      var entry = entries[i];
+      accumulation += entry.value;
       if (accumulation >= targetIndex) {
         // We've now accounted for [targetIndex] values, which includes the
         // median value.
-        return value;
+        return entry.key;
       }
     }
     throw StateError('');
@@ -53,6 +54,7 @@ class PercentileCalculator {
   /// Return a string that is suitable for sending to the analytics service.
   String toAnalyticsString() {
     var buffer = StringBuffer();
+    buffer.write(_valueCount);
     buffer.write('[');
     for (var p = 5; p <= 100; p += 5) {
       if (p > 5) {

pkg/analysis_server/test/src/analytics/percentile_calculator_test.dart

@@ -8,12 +8,12 @@ import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 void main() {
   defineReflectiveSuite(() {
-    defineReflectiveTests(PercentileTest);
+    defineReflectiveTests(PercentileCalculatorTest);
   });
 }
 
 @reflectiveTest
-class PercentileTest {
+class PercentileCalculatorTest {
   var calculator = PercentileCalculator();
 
   void test_clear() {
@@ -22,19 +22,19 @@ class PercentileTest {
     }
     calculator.clear();
     expect(calculator.toAnalyticsString(),
-        '[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]');
+        '0[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]');
   }
 
   void test_toAnalyticsString_empty() {
     expect(calculator.toAnalyticsString(),
-        '[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]');
+        '0[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]');
   }
 
   void test_toAnalyticsString_evenDistribution() {
     for (int i = 1; i <= 100; i++) {
       calculator.addValue(i);
     }
     expect(calculator.toAnalyticsString(),
-        '[5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100]');
+        '100[5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100]');
   }
 }