Un(less)conditionally schedule first callback frame when creating ticker (#16261)

* always schedule first frame when creating ticker, regardless of phase or frame

packages/flutter/lib/src/scheduler/ticker.dart

@@ -155,8 +155,9 @@ class Ticker {
     }());
     assert(_startTime == null);
     _future = new TickerFuture._();
-    if (shouldScheduleTick)
+    if (shouldScheduleTick) {
       scheduleTick();
+    }
     if (SchedulerBinding.instance.schedulerPhase.index > SchedulerPhase.idle.index &&
         SchedulerBinding.instance.schedulerPhase.index < SchedulerPhase.postFrameCallbacks.index)
       _startTime = SchedulerBinding.instance.currentFrameTimeStamp;
@@ -216,7 +217,7 @@ class Ticker {
   /// * The ticker is not active ([start] has not been called).
   /// * The ticker is not ticking, e.g. because it is [muted] (see [isTicking]).
   @protected
-  bool get shouldScheduleTick => isTicking && !scheduled;
+  bool get shouldScheduleTick => !muted && isActive && !scheduled;
 
   void _tick(Duration timeStamp) {
     assert(isTicking);
@@ -238,7 +239,6 @@ class Ticker {
   /// This should only be called if [shouldScheduleTick] is true.
   @protected
   void scheduleTick({ bool rescheduling: false }) {
-    assert(isTicking);
     assert(!scheduled);
     assert(shouldScheduleTick);
     _animationId = SchedulerBinding.instance.scheduleFrameCallback(_tick, rescheduling: rescheduling);

packages/flutter/test/scheduler/ticker_test.dart

@@ -103,4 +103,35 @@ void main() {
 
     ticker.stop();
   });
+
+  testWidgets('Ticker can be created before application unpauses', (WidgetTester tester) async {
+    final ByteData pausedMessage = const StringCodec().encodeMessage('AppLifecycleState.paused');
+    await BinaryMessages.handlePlatformMessage('flutter/lifecycle', pausedMessage, (_) {});
+    
+    int tickCount = 0;
+    void handleTick(Duration duration) {
+      tickCount += 1;
+    }
+
+    final Ticker ticker = new Ticker(handleTick);
+    ticker.start();
+
+    expect(tickCount, equals(0));
+    expect(ticker.isTicking, isFalse);
+
+    await tester.pump(const Duration(milliseconds: 10));
+
+    expect(tickCount, equals(0));
+    expect(ticker.isTicking, isFalse);
+
+    final ByteData resumedMessage = const StringCodec().encodeMessage('AppLifecycleState.resumed');
+    await BinaryMessages.handlePlatformMessage('flutter/lifecycle', resumedMessage, (_) {});
+    
+    await tester.pump(const Duration(milliseconds: 10));
+
+    expect(tickCount, equals(1));
+    expect(ticker.isTicking, isTrue);
+
+    ticker.stop();
+  });
 }