Emit compile-time error on 'const' formal parameters.

sdk/lib/_internal/compiler/implementation/warnings.dart

Index: sdk/lib/_internal/compiler/implementation/warnings.dart
diff --git a/sdk/lib/_internal/compiler/implementation/warnings.dart b/sdk/lib/_internal/compiler/implementation/warnings.dart
index 6fb63fa8829becf9bfe1d45c66e5015f149598d7..bd06786f895183766f130b48cb048047c567f3ec 100644
--- a/sdk/lib/_internal/compiler/implementation/warnings.dart
+++ b/sdk/lib/_internal/compiler/implementation/warnings.dart
@@ -550,6 +550,20 @@ main() {
   F f;
 }"""]);
 
+  static const MessageKind FORMAL_DECLARED_CONST = const MessageKind(
+      "Error: A formal parameter can't be declared const.",
+      howToFix: "Try removing 'const'.",
+      examples: const ["""
+foo(const x) {}
+main() => foo(42);
+""", """
+foo({const x}) {}
+main() => foo(42);
+""", """
+foo([const x]) {}
+main() => foo(42);
+"""]);
+
   static const MessageKind CANNOT_INSTANTIATE_TYPE_VARIABLE = const MessageKind(
       'Error: Cannot instantiate type variable "#{typeVariableName}".');