prepare for lint update of prefer_final_fields (#35059)

diff --git a/packages/flutter/lib/src/foundation/diagnostics.dart b/packages/flutter/lib/src/foundation/diagnostics.dart
index 40cb508..111d8ca 100644
--- a/packages/flutter/lib/src/foundation/diagnostics.dart
+++ b/packages/flutter/lib/src/foundation/diagnostics.dart
@@ -2707,7 +2707,7 @@
   /// [defaultValue] has type [T] or is [kNoDefaultValue].
   final Object defaultValue;
 
-  DiagnosticLevel _defaultLevel;
+  final DiagnosticLevel _defaultLevel;
 
   /// Priority level of the diagnostic used to control which diagnostics should
   /// be shown and filtered.
diff --git a/packages/flutter/lib/src/material/material.dart b/packages/flutter/lib/src/material/material.dart
index 2630f9a..2b86746 100644
--- a/packages/flutter/lib/src/material/material.dart
+++ b/packages/flutter/lib/src/material/material.dart
@@ -561,7 +561,7 @@
   /// Typically used by subclasses to call
   /// [MaterialInkController.markNeedsPaint] when they need to repaint.
   MaterialInkController get controller => _controller;
-  _RenderInkFeatures _controller;
+  final _RenderInkFeatures _controller;
 
   /// The render box whose visual position defines the frame of reference for this ink feature.
   final RenderBox referenceBox;
diff --git a/packages/flutter/lib/src/material/range_slider.dart b/packages/flutter/lib/src/material/range_slider.dart
index 2d3c84e..0fd79a7 100644
--- a/packages/flutter/lib/src/material/range_slider.dart
+++ b/packages/flutter/lib/src/material/range_slider.dart
@@ -721,7 +721,7 @@
 
   static const Duration _minimumInteractionTime = Duration(milliseconds: 500);
 
-  _RangeSliderState _state;
+  final _RangeSliderState _state;
   Animation<double> _overlayAnimation;
   Animation<double> _valueIndicatorAnimation;
   Animation<double> _enableAnimation;
diff --git a/packages/flutter/lib/src/material/slider.dart b/packages/flutter/lib/src/material/slider.dart
index a59e94d..411031c 100644
--- a/packages/flutter/lib/src/material/slider.dart
+++ b/packages/flutter/lib/src/material/slider.dart
@@ -706,7 +706,7 @@
   ];
   double get _minPreferredTrackHeight => _sliderTheme.trackHeight;
 
-  _SliderState _state;
+  final _SliderState _state;
   Animation<double> _overlayAnimation;
   Animation<double> _valueIndicatorAnimation;
   Animation<double> _enableAnimation;
diff --git a/packages/flutter/lib/src/rendering/view.dart b/packages/flutter/lib/src/rendering/view.dart
index 48b1943..17e0548 100644
--- a/packages/flutter/lib/src/rendering/view.dart
+++ b/packages/flutter/lib/src/rendering/view.dart
@@ -84,7 +84,7 @@
     markNeedsLayout();
   }
 
-  ui.Window _window;
+  final ui.Window _window;
 
   /// Whether Flutter should automatically compute the desired system UI.
   ///
diff --git a/packages/flutter/lib/src/services/platform_views.dart b/packages/flutter/lib/src/services/platform_views.dart
index 6b8ca31..790fa5c 100644
--- a/packages/flutter/lib/src/services/platform_views.dart
+++ b/packages/flutter/lib/src/services/platform_views.dart
@@ -505,9 +505,9 @@
 
   _AndroidViewState _state;
 
-  dynamic _creationParams;
+  final dynamic _creationParams;
 
-  MessageCodec<dynamic> _creationParamsCodec;
+  final MessageCodec<dynamic> _creationParamsCodec;
 
   final List<PlatformViewCreatedCallback> _platformViewCreatedCallbacks = <PlatformViewCreatedCallback>[];
 
diff --git a/packages/flutter/test/painting/image_resolution_test.dart b/packages/flutter/test/painting/image_resolution_test.dart
index 2b9c73b..096f440 100644
--- a/packages/flutter/test/painting/image_resolution_test.dart
+++ b/packages/flutter/test/painting/image_resolution_test.dart
@@ -14,7 +14,7 @@
 class TestAssetBundle extends CachingAssetBundle {
   TestAssetBundle(this._assetBundleMap);
 
-  Map<String, List<String>> _assetBundleMap;
+  final Map<String, List<String>> _assetBundleMap;
 
   Map<String, int> loadCallCount = <String, int>{};
 
diff --git a/packages/flutter_test/lib/src/widget_tester.dart b/packages/flutter_test/lib/src/widget_tester.dart
index b005436..a95f866 100644
--- a/packages/flutter_test/lib/src/widget_tester.dart
+++ b/packages/flutter_test/lib/src/widget_tester.dart
@@ -769,7 +769,7 @@
 class _TestTicker extends Ticker {
   _TestTicker(TickerCallback onTick, this._onDispose) : super(onTick);
 
-  _TickerDisposeCallback _onDispose;
+  final _TickerDisposeCallback _onDispose;
 
   @override
   void dispose() {
diff --git a/packages/flutter_tools/lib/src/android/android_emulator.dart b/packages/flutter_tools/lib/src/android/android_emulator.dart
index b0f8ad4..65a2118 100644
--- a/packages/flutter_tools/lib/src/android/android_emulator.dart
+++ b/packages/flutter_tools/lib/src/android/android_emulator.dart
@@ -30,7 +30,7 @@
   AndroidEmulator(String id, [this._properties])
     : super(id, _properties != null && _properties.isNotEmpty);
 
-  Map<String, String> _properties;
+  final Map<String, String> _properties;
 
   // Android Studio uses the ID with underscores replaced with spaces
   // for the name if displayname is not set so we do the same.
diff --git a/packages/flutter_tools/lib/src/artifacts.dart b/packages/flutter_tools/lib/src/artifacts.dart
index 319840d..1c7c178 100644
--- a/packages/flutter_tools/lib/src/artifacts.dart
+++ b/packages/flutter_tools/lib/src/artifacts.dart
@@ -260,7 +260,7 @@
 
   final String _engineSrcPath;
   final String engineOutPath; // TODO(goderbauer): This should be private.
-  String _hostEngineOutPath;
+  final String _hostEngineOutPath;
 
   @override
   String getArtifactPath(Artifact artifact, { TargetPlatform platform, BuildMode mode }) {
diff --git a/packages/flutter_tools/lib/src/compile.dart b/packages/flutter_tools/lib/src/compile.dart
index 0a577a1..93ea80a 100644
--- a/packages/flutter_tools/lib/src/compile.dart
+++ b/packages/flutter_tools/lib/src/compile.dart
@@ -450,8 +450,8 @@
   String _sdkRoot;
   Process _server;
   final StdoutHandler _stdoutHandler;
-  String _initializeFromDill;
-  bool _unsafePackageSerialization;
+  final String _initializeFromDill;
+  final bool _unsafePackageSerialization;
   final List<String> _experimentalFlags;
   bool _compileRequestNeedsConfirmation = false;
 
diff --git a/packages/flutter_tools/lib/src/devfs.dart b/packages/flutter_tools/lib/src/devfs.dart
index e15fb5c..7a28775 100644
--- a/packages/flutter_tools/lib/src/devfs.dart
+++ b/packages/flutter_tools/lib/src/devfs.dart
@@ -369,7 +369,7 @@
   final _DevFSHttpWriter _httpWriter;
   final String fsName;
   final Directory rootDirectory;
-  String _packagesFilePath;
+  final String _packagesFilePath;
   final Set<String> assetPathsToEvict = <String>{};
   List<Uri> sources = <Uri>[];
   DateTime lastCompiled;
diff --git a/packages/flutter_tools/lib/src/fuchsia/fuchsia_device.dart b/packages/flutter_tools/lib/src/fuchsia/fuchsia_device.dart
index 8576789..d6513f6 100644
--- a/packages/flutter_tools/lib/src/fuchsia/fuchsia_device.dart
+++ b/packages/flutter_tools/lib/src/fuchsia/fuchsia_device.dart
@@ -59,8 +59,8 @@
   // \S matches non-whitespace characters.
   static final RegExp _flutterLogOutput = RegExp(r'INFO: \S+\(flutter\): ');
 
-  FuchsiaDevice _device;
-  ApplicationPackage _app;
+  final FuchsiaDevice _device;
+  final ApplicationPackage _app;
 
   @override
   String get name => _device.name;
diff --git a/packages/flutter_tools/test/runner/flutter_command_test.dart b/packages/flutter_tools/test/runner/flutter_command_test.dart
index bc6582b..ba9e975 100644
--- a/packages/flutter_tools/test/runner/flutter_command_test.dart
+++ b/packages/flutter_tools/test/runner/flutter_command_test.dart
@@ -355,7 +355,7 @@
   @override
   final bool ephemeral;
 
-  bool _isSupported;
+  final bool _isSupported;
 
   @override
   bool isSupportedForProject(FlutterProject flutterProject) => _isSupported;