Experimental flags for hot reloads (#26988)

* First pass at incremental exp flags

* adkfgjh

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

@@ -333,6 +333,11 @@ 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 = null;
+    if (argParser.options.containsKey(FlutterOptions.kEnableExperiment) &&
+        argResults[FlutterOptions.kEnableExperiment] != null) {
+      expFlags = argResults[FlutterOptions.kEnableExperiment];
+    }
     final List<FlutterDevice> flutterDevices = devices.map<FlutterDevice>((Device device) {
       return FlutterDevice(
         device,
@@ -341,6 +346,7 @@ 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

@@ -332,7 +332,8 @@ 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,
@@ -342,7 +343,8 @@ 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/';
@@ -358,6 +360,7 @@ class ResidentCompiler {
   final _StdoutHandler _stdoutHandler;
   String _initializeFromDill;
   bool _unsafePackageSerialization;
+  final List<String> _experimentalFlags;
 
   final StreamController<_CompilationRequest> _controller;
 
@@ -470,6 +473,10 @@ class ResidentCompiler {
     if (_unsafePackageSerialization == true) {
       command.add('--unsafe-package-serialization');
     }
+    if (_experimentalFlags != null) {
+      var 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;