Implement --fatal=errors.

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

Index: pkg/front_end/lib/src/fasta/messages.dart
diff --git a/pkg/front_end/lib/src/fasta/messages.dart b/pkg/front_end/lib/src/fasta/messages.dart
index a4e4939fd401865d9ea6f321bd02275245977b83..e6a65908e893be5bef1f14df7715b85aba58931c 100644
--- a/pkg/front_end/lib/src/fasta/messages.dart
+++ b/pkg/front_end/lib/src/fasta/messages.dart
@@ -25,11 +25,19 @@ const bool hideNits = false;
 
 const bool hideWarnings = false;
 
+bool get areErrorsFatal => CompilerContext.current.options.areErrorsFatal;
+
+bool get areNitsFatal => CompilerContext.current.options.areNitsFatal;
+
+bool get areWarningsFatal => CompilerContext.current.options.areWarningsFatal;
+
+bool get isVerbose => CompilerContext.current.options.verbose;
+
 void warning(Uri uri, int charOffset, String message) {
   if (hideWarnings) return;
   print(format(uri, charOffset, colorWarning("Warning: $message")));
-  if (CompilerContext.current.options.areWarningsFatal) {
-    if (CompilerContext.current.options.verbose) print(StackTrace.current);
+  if (areWarningsFatal) {
+    if (isVerbose) print(StackTrace.current);
     throw new InputError(
         uri, charOffset, "Compilation aborted due to fatal warnings.");
   }
@@ -38,8 +46,8 @@ void warning(Uri uri, int charOffset, String message) {
 void nit(Uri uri, int charOffset, String message) {
   if (hideNits) return;
   print(format(uri, charOffset, colorNit("Nit: $message")));
-  if (CompilerContext.current.options.areNitsFatal) {
-    if (CompilerContext.current.options.verbose) print(StackTrace.current);
+  if (areNitsFatal) {
+    if (isVerbose) print(StackTrace.current);
     throw new InputError(
         uri, charOffset, "Compilation aborted due to fatal nits.");
   }