tweak the doctor check for host compatibility (#9720)

packages/flutter_tools/lib/src/doctor.dart

@@ -44,7 +44,6 @@ class Doctor {
     if (_validators == null) {
       _validators = <DoctorValidator>[];
       _validators.add(new _FlutterValidator());
-      _validators.add(new _HostExecutableValidator());
 
       if (_androidWorkflow.appliesToHostPlatform)
         _validators.add(_androidWorkflow);
@@ -213,39 +212,26 @@ class _FlutterValidator extends DoctorValidator {
     ));
     messages.add(new ValidationMessage('Engine revision ${version.engineRevisionShort}'));
     messages.add(new ValidationMessage('Tools Dart version ${version.dartSdkVersion}'));
+    final String genSnapshotPath =
+      artifacts.getArtifactPath(Artifact.genSnapshot);
+
+    // Check that the binaries we downloaded for this platform actually run on it.
+    if (!_genSnapshotRuns(genSnapshotPath)) {
+      messages.add(new ValidationMessage.error('Downloaded executables cannot execute '
+          'on host (see https://github.com/flutter/flutter/issues/6207 for more information)'));
+    }
 
     return new ValidationResult(valid, messages,
       statusInfo: 'on ${os.name}, channel ${version.channel}');
   }
 }
 
-class _HostExecutableValidator extends DoctorValidator {
-  _HostExecutableValidator() : super('Host Executable Compatibility');
-
-  bool _genSnapshotRuns(String genSnapshotPath) {
-    final int kExpectedExitCode = 255;
-    try {
-      return processManager.runSync(<String>[genSnapshotPath]).exitCode == kExpectedExitCode;
-    } catch (error) {
-      return false;
-    }
-  }
-
-  @override
-  Future<ValidationResult> validate() async {
-    final String genSnapshotPath =
-      artifacts.getArtifactPath(Artifact.genSnapshot);
-    final List<ValidationMessage> messages = <ValidationMessage>[];
-    final bool hostExecutablesRun = _genSnapshotRuns(genSnapshotPath);
-    final ValidationType valid = hostExecutablesRun ? ValidationType.installed : ValidationType.missing;
-
-    if (hostExecutablesRun) {
-      messages.add(new ValidationMessage('Downloaded executables execute on host'));
-    } else {
-      messages.add(new ValidationMessage.error(
-        'Downloaded executables cannot execute on host. See https://github.com/flutter/flutter/issues/6207 for more information'));
-    }
-    return new ValidationResult(valid, messages);
+bool _genSnapshotRuns(String genSnapshotPath) {
+  final int kExpectedExitCode = 255;
+  try {
+    return processManager.runSync(<String>[genSnapshotPath]).exitCode == kExpectedExitCode;
+  } catch (error) {
+    return false;
   }
 }