Check that non-abstract classes implement all methods.

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

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart2js;
 
 const DONT_KNOW_HOW_TO_FIX = "";
 
 /**
  * The messages in this file should meet the following guide lines:
@@ skipping 1342 matching lines @@
       const MessageKind(
           "Error: '#{keyword}' is a reserved word and can't be used here.",
           howToFix: "Try using a different name.",
           examples: const ["do() {} main() {}"]);
 
   static const MessageKind UNUSED_METHOD = const MessageKind(
       "Hint: The method '#{method_name}' is never called.",
       howToFix: "Consider deleting it.",
       examples: const ["deadCode() {} main() {}"]);
 
+  static const MessageKind UNIMPLEMENTED_METHOD = const MessageKind(
+      "Warning: '#{class_name}' doesn't implement '#{member_name}'.",
+      howToFix: "Try adding an implementation of '#{member_name}'.",
+      examples: const ["""
+abstract class I {
+  m();
+}
+
+class C implements I {}
+
+class D implements I {
+  m() {}
+}
+
+main() {
+ new D().m();
+ new C();
+}
+""", """
+abstract class I {
+  m();
+}
+
+class C extends I {}
+
+class D extends I {
+  m() {}
+}
+
+main() {
+ new D().m();
+ new C();
+}
+"""]);
+
   static const MessageKind COMPILER_CRASHED = const MessageKind(
       "Error: The compiler crashed when compiling this element.");
 
   static const MessageKind PLEASE_REPORT_THE_CRASH = const MessageKind('''
 The compiler is broken.
 
 When compiling the above element, the compiler crashed. It is not
 possible to tell if this is caused by a problem in your program or
 not. Regardless, the compiler should not crash.
 
@@ skipping 220 matching lines @@
 
 class CompileTimeConstantError extends Diagnostic {
   CompileTimeConstantError(MessageKind kind, Map arguments, bool terse)
     : super(kind, arguments, terse);
 }
 
 class CompilationError extends Diagnostic {
   CompilationError(MessageKind kind, Map arguments, bool terse)
     : super(kind, arguments, terse);
 }