Add a compile time error for non-static const fields

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 435b59499b3617b33bf19007f2ceeb9c08144342..653cdbed00721f745b5bc9650d2996c83efc2c54 100644
--- a/sdk/lib/_internal/compiler/implementation/warnings.dart
+++ b/sdk/lib/_internal/compiler/implementation/warnings.dart
@@ -991,6 +991,16 @@ main() => new C();"""]);
   static const MessageKind ILLEGAL_FINAL_METHOD_MODIFIER = const MessageKind(
       "Cannot have final modifier on method.");
 
+  static const MessageKind ILLEGAL_CONST_FIELD_MODIFIER = const MessageKind(
+      "Cannot have const modifier on non-static field.",
+      howToFix: "Try adding a static modifier, or removing the const modifier.",
+      examples: const ["""
+class C {
+  const int a = 1;
+}
+
+main() => new C();"""]);
+
   static const MessageKind ILLEGAL_CONSTRUCTOR_MODIFIERS = const MessageKind(
       "Illegal constructor modifiers: '#{modifiers}'.");