Check for non-final field in the face of const constructors.

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 1694daa7e58bae9c51aab92e5eac028d31e8463c..c108cf83ab36a965fee6166061a65fefb4c3a005 100644
--- a/sdk/lib/_internal/compiler/implementation/warnings.dart
+++ b/sdk/lib/_internal/compiler/implementation/warnings.dart
@@ -282,6 +282,29 @@ main() => new C();"""]);
   static const MessageKind CONST_CALLS_NON_CONST = const MessageKind(
       'Error: "const" constructor cannot call a non-const constructor.');
 
+  static const MessageKind CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS =
+      const MessageKind(
+          "Error: Can't declare constructor 'const' on class #{className} "
+          "because the class contains non-final instance fields.",
+          howToFix: "Try making all fields final.",
+          examples: const ["""
+class C {
+  // 'a' must be declared final to allow for the const constructor.
+  var a;
+  const C(this.a);
+}
+
+main() => new C(0);"""]);
+
+  static const MessageKind CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS_FIELD =
+      const MessageKind('Info: This non-final field prevents using const '
+                        'constructors.');
+
+  static const MessageKind CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS_CONSTRUCTOR =
+      const MessageKind('Info: This const constructor is not allowed due to '
+                        'non-final fields.');
+
+
   static const MessageKind INITIALIZING_FORMAL_NOT_ALLOWED = const MessageKind(
       'Error: Initializing formal parameter only allowed in generative '
       'constructor.');