Add 90th and 99th percentile frame rasterize time for timeline_summary (#18881)

Our first step towards https://github.com/flutter/flutter/issues/18727

packages/flutter_driver/lib/src/driver/timeline_summary.dart

@@ -60,6 +60,13 @@ class TimelineSummary {
     return _maxInMillis(_extractDuration(_extractGpuRasterizerDrawEvents()));
   }
 
+  /// The [p]-th percentile frame rasterization time in milliseconds.
+  ///
+  /// Returns null if no frames were recorded.
+  double computePercentileFrameRasterizerTimeMillis(double p) {
+    return _percentileInMillis(_extractDuration(_extractGpuRasterizerDrawEvents()), p);
+  }
+
   /// The number of frames that missed the [kBuildBudget] on the GPU and
   /// therefore are in the danger of missing frames.
   int computeMissedFrameRasterizerBudgetCount([Duration frameBuildBudget = kBuildBudget]) => _extractGpuRasterizerDrawEvents()
@@ -76,6 +83,8 @@ class TimelineSummary {
       'worst_frame_build_time_millis': computeWorstFrameBuildTimeMillis(),
       'missed_frame_build_budget_count': computeMissedFrameBuildBudgetCount(),
       'average_frame_rasterizer_time_millis': computeAverageFrameRasterizerTimeMillis(),
+      '90th_percentile_frame_rasterizer_time_millis': computePercentileFrameRasterizerTimeMillis(90.0),
+      '99th_percentile_frame_rasterizer_time_millis': computePercentileFrameRasterizerTimeMillis(99.0),
       'worst_frame_rasterizer_time_millis': computeWorstFrameRasterizerTimeMillis(),
       'missed_frame_rasterizer_budget_count': computeMissedFrameRasterizerBudgetCount(),
       'frame_count': countFrames(),
@@ -159,6 +168,17 @@ class TimelineSummary {
     return total / durations.length;
   }
 
+  double _percentileInMillis(Iterable<Duration> durations, double percentile) {
+    if (durations.isEmpty)
+      return null;
+
+    assert(percentile >= 0.0 && percentile <= 100.0);
+    final List<double> doubles = durations.map<double>((Duration duration) => duration.inMilliseconds.toDouble()).toList();
+    doubles.sort();
+    return doubles[((doubles.length - 1) * (percentile / 100)).round()];
+
+  }
+
   double _maxInMillis(Iterable<Duration> durations) {
     if (durations.isEmpty)
       return null;

packages/flutter_driver/test/src/timeline_summary_test.dart

@@ -31,6 +31,17 @@ void main() {
       'name': 'GPURasterizer::Draw', 'ph': 'E', 'ts': timeStamp
     };
 
+    List<Map<String, dynamic>> rasterizeTimeSequenceInMillis(List<int> sequence) {
+      final List<Map<String, dynamic>> result = <Map<String, dynamic>>[];
+      int t = 0;
+      for(int duration in sequence) {
+        result.add(begin(t));
+        t += duration * 1000;
+        result.add(end(t));
+      }
+      return result;
+    }
+
     group('frame_count', () {
       test('counts frames', () {
         expect(
@@ -174,6 +185,44 @@ void main() {
       });
     });
 
+    group('percentile_frame_rasterizer_time_millis', () {
+      test('returns null when there is no data', () {
+        expect(summarize(<Map<String, dynamic>>[]).computeWorstFrameRasterizerTimeMillis(), isNull);
+      });
+
+      const List<List<int>> sequences = <List<int>>[
+        <int>[1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
+        <int>[1, 2, 3, 4, 5],
+        <int>[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
+      ];
+
+      const List<int> p90s = <int>[
+        9,
+        5,
+        18
+      ];
+
+      test('computes 90th frame rasterizer time in milliseconds', () {
+        for(int i = 0; i < sequences.length; ++i) {
+          expect(
+            summarize(rasterizeTimeSequenceInMillis(sequences[i])).computePercentileFrameRasterizerTimeMillis(90.0),
+            p90s[i]
+          );
+        }
+      });
+
+      test('compute 99th frame rasterizer time in milliseconds', () {
+        final List<int> sequence = <int>[];
+        for(int i = 1; i <= 100; ++i) {
+          sequence.add(i);
+        }
+        expect(
+          summarize(rasterizeTimeSequenceInMillis(sequence)).computePercentileFrameRasterizerTimeMillis(99.0),
+          99
+        );
+      });
+    });
+
     group('computeMissedFrameRasterizerBudgetCount', () {
       test('computes the number of missed rasterizer budgets', () {
         final TimelineSummary summary = summarize(<Map<String, dynamic>>[
@@ -202,6 +251,8 @@ void main() {
             'worst_frame_build_time_millis': 11.0,
             'missed_frame_build_budget_count': 2,
             'average_frame_rasterizer_time_millis': 8.0,
+            '90th_percentile_frame_rasterizer_time_millis': 12.0,
+            '99th_percentile_frame_rasterizer_time_millis': 12.0,
             'worst_frame_rasterizer_time_millis': 12.0,
             'missed_frame_rasterizer_budget_count': 2,
             'frame_count': 3,
@@ -250,6 +301,8 @@ void main() {
           'worst_frame_build_time_millis': 11.0,
           'missed_frame_build_budget_count': 2,
           'average_frame_rasterizer_time_millis': 8.0,
+          '90th_percentile_frame_rasterizer_time_millis': 12.0,
+          '99th_percentile_frame_rasterizer_time_millis': 12.0,
           'worst_frame_rasterizer_time_millis': 12.0,
           'missed_frame_rasterizer_budget_count': 2,
           'frame_count': 3,