[timeline] Sort timeline events before summarizing (#55771)

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

@@ -34,12 +34,8 @@ class TimelineEvent {
       json['ph'] as String,
       json['pid'] as int,
       json['tid'] as int,
-      json['dur'] != null
-        ? Duration(microseconds: json['dur'] as int)
-        : null,
-      json['tdur'] != null
-        ? Duration(microseconds: json['tdur'] as int)
-        : null,
+      json['dur'] != null ? Duration(microseconds: json['dur'] as int) : null,
+      json['tdur'] != null ? Duration(microseconds: json['tdur'] as int) : null,
       json['ts'] as int,
       json['tts'] as int,
       json['args'] as Map<String, dynamic>,
@@ -124,11 +120,32 @@ class TimelineEvent {
 List<TimelineEvent> _parseEvents(Map<String, dynamic> json) {
   final List<dynamic> jsonEvents = json['traceEvents'] as List<dynamic>;
 
-  if (jsonEvents == null)
+  if (jsonEvents == null) {
     return null;
+  }
 
   // TODO(vegorov): use instance method version of castFrom when it is available.
-  return Iterable.castFrom<dynamic, Map<String, dynamic>>(jsonEvents)
-    .map<TimelineEvent>((Map<String, dynamic> eventJson) => TimelineEvent(eventJson))
-    .toList();
+  final List<TimelineEvent> timelineEvents =
+      Iterable.castFrom<dynamic, Map<String, dynamic>>(jsonEvents)
+          .map<TimelineEvent>(
+              (Map<String, dynamic> eventJson) => TimelineEvent(eventJson))
+          .toList();
+
+  timelineEvents.sort((TimelineEvent e1, TimelineEvent e2) {
+    final int ts1 = e1.timestampMicros;
+    final int ts2 = e2.timestampMicros;
+    if (ts1 == null) {
+      if (ts2 == null) {
+        return 0;
+      } else {
+        return -1;
+      }
+    } else if (ts2 == null) {
+      return 1;
+    } else {
+      return ts1.compareTo(ts2);
+    }
+  });
+
+  return timelineEvents;
 }

packages/flutter_driver/test/src/real_tests/timeline_test.dart

@@ -32,7 +32,7 @@ void main() {
 
       expect(timeline.events, hasLength(2));
 
-      final TimelineEvent e1 = timeline.events[0];
+      final TimelineEvent e1 = timeline.events[1];
       expect(e1.name, 'test event');
       expect(e1.category, 'test category');
       expect(e1.phase, 'B');
@@ -44,7 +44,7 @@ void main() {
       expect(e1.threadTimestampMicros, 567);
       expect(e1.arguments, <String, dynamic>{'arg1': true});
 
-      final TimelineEvent e2 = timeline.events[1];
+      final TimelineEvent e2 = timeline.events[0];
       expect(e2.name, isNull);
       expect(e2.category, isNull);
       expect(e2.phase, isNull);
@@ -56,5 +56,59 @@ void main() {
       expect(e2.threadTimestampMicros, isNull);
       expect(e2.arguments, isNull);
     });
+
+    test('sorts JSON', () {
+      final Timeline timeline = Timeline.fromJson(<String, dynamic>{
+        'traceEvents': <Map<String, dynamic>>[
+          <String, dynamic>{
+            'name': 'test event 1',
+            'ts': 457,
+          },
+          <String, dynamic>{
+            'name': 'test event 2',
+            'ts': 456,
+          },
+        ],
+      });
+
+      expect(timeline.events, hasLength(2));
+      expect(timeline.events[0].timestampMicros, equals(456));
+      expect(timeline.events[1].timestampMicros, equals(457));
+      expect(timeline.events[0].name, equals('test event 2'));
+      expect(timeline.events[1].name, equals('test event 1'));
+    });
+
+    test('sorts JSON nulls first', () {
+      final Timeline timeline = Timeline.fromJson(<String, dynamic>{
+        'traceEvents': <Map<String, dynamic>>[
+          <String, dynamic>{
+            'name': 'test event 0',
+            'ts': null,
+          },
+          <String, dynamic>{
+            'name': 'test event 1',
+            'ts': 457,
+          },
+          <String, dynamic>{
+            'name': 'test event 2',
+            'ts': 456,
+          },
+          <String, dynamic>{
+            'name': 'test event 3',
+            'ts': null,
+          },
+        ],
+      });
+
+      expect(timeline.events, hasLength(4));
+      expect(timeline.events[0].timestampMicros, isNull);
+      expect(timeline.events[1].timestampMicros, isNull);
+      expect(timeline.events[2].timestampMicros, equals(456));
+      expect(timeline.events[3].timestampMicros, equals(457));
+      expect(timeline.events[0].name, equals('test event 0'));
+      expect(timeline.events[1].name, equals('test event 3'));
+      expect(timeline.events[2].name, equals('test event 2'));
+      expect(timeline.events[3].name, equals('test event 1'));
+    });
   });
 }