Roll engine to f3ff83a5db71262d240aa5337a2a9a22c73c4749. (dart roll). (#21143)

* Roll engine to 56139397e6ae1257bdabd1ef79ff7aca96c67d4.6

Changes since last roll:
```
56139397e Roll src/third_party/skia 7ba1d64f0706..5f0726b01019 (12 commits) (#6104)
47a1ce0e6 Allow embedders to set the root surface transformation. (#6085)
```

* Roll engine to f3ff83a5db71262d240aa5337a2a9a22c73c4749. (dart roll).

* Add const

* Add ignore analyzer prefer_const_constructors_in_immutables

bin/internal/engine.version

-56bad48ab2eda51906e27adc1f61b89f26224bbc
+f3ff83a5db71262d240aa5337a2a9a22c73c4749

packages/flutter/lib/src/widgets/platform_view.dart

@@ -50,7 +50,7 @@ class AndroidView extends StatefulWidget {
   ///
   /// The `viewType`, `hitTestBehavior`, and `gestureRecognizers` parameters must not be null.
   /// If `creationParams` is not null then `creationParamsCodec` must not be null.
-  AndroidView({
+  AndroidView({ // ignore: prefer_const_constructors_in_immutables
     Key key,
     @required this.viewType,
     this.onPlatformViewCreated,

packages/flutter/lib/src/widgets/scroll_view.dart

@@ -50,7 +50,7 @@ abstract class ScrollView extends StatelessWidget {
   /// Creates a widget that scrolls.
   ///
   /// If the [primary] argument is true, the [controller] must be null.
-  ScrollView({
+  ScrollView({ // ignore: prefer_const_constructors_in_immutables
     Key key,
     this.scrollDirection = Axis.vertical,
     this.reverse = false,

packages/flutter/lib/src/widgets/single_child_scroll_view.dart

@@ -183,7 +183,7 @@ import 'scrollable.dart';
 /// * [Scrollable], which handles arbitrary scrolling effects.
 class SingleChildScrollView extends StatelessWidget {
   /// Creates a box in which a single widget can be scrolled.
-  SingleChildScrollView({
+  SingleChildScrollView({ // ignore: prefer_const_constructors_in_immutables
     Key key,
     this.scrollDirection = Axis.vertical,
     this.reverse = false,