Implement override checks for methods.

pkg/front_end/lib/src/fasta/colors.dart

Index: pkg/front_end/lib/src/fasta/colors.dart
diff --git a/pkg/front_end/lib/src/fasta/colors.dart b/pkg/front_end/lib/src/fasta/colors.dart
index 753da3d181688a4ddb34891097516cfbd511f231..301e9ad281c23d22756107d461da585ef8cc1c83 100644
--- a/pkg/front_end/lib/src/fasta/colors.dart
+++ b/pkg/front_end/lib/src/fasta/colors.dart
@@ -101,10 +101,11 @@ bool computeEnableColors(CompilerContext context) {
   bool ansiSupported;
   try {
     ansiSupported = Platform.ansiSupported;
-  } on NoSuchMethodError catch (e) {
+  } on NoSuchMethodError {
     // Ignored: We're running on an older version of the Dart VM which doesn't
     // implement `ansiSupported`.
   }
+
   if (ansiSupported == false) {
     if (context.options.verbose) {
       print("Not enabling colors, 'Platform.ansiSupported' is false.");