Add support for experimental flags during hot reload. (#27252)

* Add support for experimental flags during hot reload.

packages/flutter_tools/lib/src/commands/run.dart

@@ -339,6 +339,12 @@ class RunCommand extends RunCommandBase {
       throwToolExit('Error: --train is only allowed when running as --dynamic --profile '
           '(recommended) or --debug (may include unwanted debug symbols).');
 
+    List<String> expFlags;
+    if (argParser.options.containsKey(FlutterOptions.kEnableExperiment) &&
+        argResults[FlutterOptions.kEnableExperiment].isNotEmpty) {
+      expFlags = argResults[FlutterOptions.kEnableExperiment];
+    }
+
     final List<FlutterDevice> flutterDevices = devices.map<FlutterDevice>((Device device) {
       return FlutterDevice(
         device,
@@ -347,6 +353,7 @@ class RunCommand extends RunCommandBase {
         fileSystemRoots: argResults['filesystem-root'],
         fileSystemScheme: argResults['filesystem-scheme'],
         viewFilter: argResults['isolate-filter'],
+        experimentalFlags: expFlags,
       );
     }).toList();
 

packages/flutter_tools/lib/src/compile.dart

@@ -341,7 +341,8 @@ class ResidentCompiler {
     CompilerMessageConsumer compilerMessageConsumer = printError,
     String initializeFromDill,
     TargetModel targetModel = TargetModel.flutter,
-    bool unsafePackageSerialization
+    bool unsafePackageSerialization,
+    List<String> experimentalFlags,
   }) : assert(_sdkRoot != null),
        _trackWidgetCreation = trackWidgetCreation,
        _packagesPath = packagesPath,
@@ -351,7 +352,8 @@ class ResidentCompiler {
        _stdoutHandler = StdoutHandler(consumer: compilerMessageConsumer),
        _controller = StreamController<_CompilationRequest>(),
        _initializeFromDill = initializeFromDill,
-       _unsafePackageSerialization = unsafePackageSerialization {
+       _unsafePackageSerialization = unsafePackageSerialization,
+       _experimentalFlags = experimentalFlags {
     // This is a URI, not a file path, so the forward slash is correct even on Windows.
     if (!_sdkRoot.endsWith('/'))
       _sdkRoot = '$_sdkRoot/';
@@ -367,6 +369,7 @@ class ResidentCompiler {
   final StdoutHandler _stdoutHandler;
   String _initializeFromDill;
   bool _unsafePackageSerialization;
+  final List<String> _experimentalFlags;
 
   final StreamController<_CompilationRequest> _controller;
 
@@ -479,6 +482,10 @@ class ResidentCompiler {
     if (_unsafePackageSerialization == true) {
       command.add('--unsafe-package-serialization');
     }
+    if ((_experimentalFlags != null) && _experimentalFlags.isNotEmpty) {
+      final String expFlags = _experimentalFlags.join(',');
+      command.add('--enable-experiment=$expFlags');
+    }
     printTrace(command.join(' '));
     _server = await processManager.start(command);
     _server.stdout

packages/flutter_tools/lib/src/resident_runner.dart

@@ -35,6 +35,7 @@ class FlutterDevice {
     this.fileSystemScheme,
     this.viewFilter,
     TargetModel targetModel = TargetModel.flutter,
+    List<String> experimentalFlags,
     ResidentCompiler generator,
   }) : assert(trackWidgetCreation != null),
        generator = generator ?? ResidentCompiler(
@@ -43,6 +44,7 @@ class FlutterDevice {
          fileSystemRoots: fileSystemRoots,
          fileSystemScheme: fileSystemScheme,
          targetModel: targetModel,
+	 experimentalFlags: experimentalFlags,
        );
 
   final Device device;