Initialize the lifecycle state with initial state in window. Roll engine (19 commits) (#28688)

git log --oneline --no-merges f4951df193a7966f9ed4da43d555eee0913d84d1..a48cd16e077778a7aa5908e4faa4da07714260f2
a48cd16e0 Update a11y word forward/back enum names (https://github.com/flutter/engine/pull/8073)
b5f59ed89 Delay the vsync callback till the frame start time specified by embedder. (https://github.com/flutter/engine/pull/8072)
7426305f5 Mark const extern (https://github.com/flutter/engine/pull/8077)
d3f6d7a21 only partial rule revert (https://github.com/flutter/engine/pull/8078)
d71bfe58d Only build a full Dart SDK when building for the host system (https://github.com/flutter/engine/pull/8071)
de90dbff7 Refactor web configuration/ Add dartdevc (https://github.com/flutter/engine/pull/7978)
ff46dd38f Roll src/third_party/skia 4c1ea43a79b5..88b8d1124b72 (8 commits) (https://github.com/flutter/engine/pull/8070)
80c6dd286 Roll src/third_party/skia 692122e3ef23..4c1ea43a79b5 (3 commits) (https://github.com/flutter/engine/pull/8069)
68ed654ea Roll src/third_party/skia 3c957d575c58..692122e3ef23 (6 commits) (https://github.com/flutter/engine/pull/8067)
ca0bac4fb Revert "add signal to pointer kinds" (https://github.com/flutter/engine/pull/8066)
3fb627f2c add signal to pointer kinds (https://github.com/flutter/engine/pull/8065)
5a06afa2a Roll src/third_party/skia 801a9c16d81e..3c957d575c58 (19 commits) (https://github.com/flutter/engine/pull/8063)
a93d99db9 A11y callback (https://github.com/flutter/engine/pull/8005)
3661d5e43 Re-land "Buffer lifecycle in WindowData" (https://github.com/flutter/engine/pull/8032)
471a2c89a Send scroll events from the macOS shell (https://github.com/flutter/engine/pull/8056)
2fe9c9b5f Roll src/third_party/skia 72542816cadb..801a9c16d81e (46 commits) (https://github.com/flutter/engine/pull/8060)
3335764ae Skip skp files in license check (https://github.com/flutter/engine/pull/8050)
7f16789b2 Remove redundant thread checker in FML. (https://github.com/flutter/engine/pull/8053)
840c5233a Correct URL for Cirrus CI build status badge (https://github.com/flutter/engine/pull/8054)
57c120a29 remove extra source files (https://github.com/flutter/engine/pull/8052)
4773375c6 Used named conditionals for platform specific dependencies and suppress Android and Windows hooks on Mac. (https://github.com/flutter/engine/pull/8051)
70a18b515 Add clang static analysis support to gn wrapper (https://github.com/flutter/engine/pull/8047)
b30f9897b Improve elevation bounds for physical shape layers (https://github.com/flutter/engine/pull/8044)
e37bd27b4 Fix weak pointer use violations in shell and platform view. (https://github.com/flutter/engine/pull/8046)
dd80fc9ff Add engine support for scrollwheel events (https://github.com/flutter/engine/pull/7494)

bin/internal/engine.version

-f4951df193a7966f9ed4da43d555eee0913d84d1
+a48cd16e077778a7aa5908e4faa4da07714260f2

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

@@ -193,6 +193,7 @@ mixin SchedulerBinding on BindingBase, ServicesBinding {
     window.onBeginFrame = _handleBeginFrame;
     window.onDrawFrame = _handleDrawFrame;
     SystemChannels.lifecycle.setMessageHandler(_handleLifecycleMessage);
+    readInitialLifecycleStateFromNativeWindow();
   }
 
   /// The current [SchedulerBinding], if one has been created.
@@ -225,6 +226,23 @@ mixin SchedulerBinding on BindingBase, ServicesBinding {
   AppLifecycleState get lifecycleState => _lifecycleState;
   AppLifecycleState _lifecycleState;
 
+  /// Initializes the [lifecycleState] with the [initialLifecycleState] from the
+  /// window.
+  ///
+  /// Once the [lifecycleState] is populated through any means (including this
+  /// method), this method will do nothing. This is because the
+  /// [initialLifecycleState] may already be stale and it no longer makes sense
+  /// to use the initial state at dart vm startup as the current state anymore.
+  ///
+  /// The latest state should be obtained by subscribing to
+  /// [WidgetsBindingObserver.didChangeAppLifecycleState].
+  @protected
+  void readInitialLifecycleStateFromNativeWindow() {
+    if (_lifecycleState == null && _parseAppLifecycleMessage(window.initialLifecycleState) != null) {
+      _handleLifecycleMessage(window.initialLifecycleState);
+    }
+  }
+
   /// Called when the application lifecycle state changes.
   ///
   /// Notifies all the observers using

packages/flutter/test/scheduler/lifecycle_test.dart

+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/scheduler.dart';
+
+void main() {
+  testWidgets('initialLifecycleState is used to init state paused', (WidgetTester tester) async {
+    // The lifecycleState is null initially in tests as there is no
+    // initialLifecycleState.
+    expect(SchedulerBinding.instance.lifecycleState, equals(null));
+    // Mock the Window to provide paused as the AppLifecycleState
+    final TestWidgetsFlutterBinding binding = tester.binding;
+    // Use paused as the initial state.
+    binding.window.initialLifecycleStateTestValue = 'AppLifecycleState.paused';
+    binding.readTestInitialLifecycleStateFromNativeWindow(); // Re-attempt the initializaiton.
+
+    // The lifecycleState should now be the state we passed above,
+    // even though no lifecycle event was fired from the platform.
+    expect(SchedulerBinding.instance.lifecycleState.toString(), equals('AppLifecycleState.paused'));
+  });
+}

packages/flutter_test/lib/src/binding.dart

@@ -257,6 +257,12 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
     });
   }
 
+  /// Re-attempts the initialization of the lifecycle state after providing
+  /// test values in [TestWindow.initialLifecycleStateTestValue].
+  void readTestInitialLifecycleStateFromNativeWindow() {
+    readInitialLifecycleStateFromNativeWindow();
+  }
+
   Size _surfaceSize;
 
   /// Artificially changes the surface size to `size` on the Widget binding,

packages/flutter_test/lib/src/window.dart

@@ -151,6 +151,14 @@ class TestWindow implements Window {
     _window.onLocaleChanged = callback;
   }
 
+  @override
+  String get initialLifecycleState => _initialLifecycleStateTestValue;
+  String _initialLifecycleStateTestValue;
+  /// Sets a faked initialLifecycleState for testing.
+  set initialLifecycleStateTestValue(String state) {
+    _initialLifecycleStateTestValue = state;
+  }
+
   @override
   double get textScaleFactor => _textScaleFactorTestValue ?? _window.textScaleFactor;
   double _textScaleFactorTestValue;