Issue 5084. Report error if a type name appears multiple times in an implements clause

compiler/java/com/google/dart/compiler/resolver/ResolverErrorCode.java

 // Copyright (c) 2012, 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.
 package com.google.dart.compiler.resolver;
 
 import com.google.dart.compiler.ErrorCode;
 import com.google.dart.compiler.ErrorSeverity;
 import com.google.dart.compiler.SubSystem;
 
 /**
@@ skipping 65 matching lines @@
       "default class must have the same type parameters as declared in the interface"),
   DEFAULT_CONSTRUCTOR_UNRESOLVED("Cannot resolve constructor with name '%s' in default class '%s'"),
   DEFAULT_CONSTRUCTOR_NUMBER_OF_REQUIRED_PARAMETERS(
       "Constructor '%s' in '%s' has %s required parameters, doesn't match '%s' in '%s' with %s"),
   DEFAULT_CONSTRUCTOR_NAMED_PARAMETERS(
       "Constructor '%s' in '%s' has named parameters %s, doesn't match '%s' in '%s' with %s"),
   DEFAULT_MUST_SPECIFY_CLASS("default must indicate a class, not an interface"),
   DEPRECATED_MAP_LITERAL_SYNTAX(ErrorSeverity.WARNING,
       "Deprecated Map literal syntax. Both String (as key) and value type arguments required."),
   DID_YOU_MEAN_NEW("%1$s is a %2$s. Did you mean (new %1$s)?"),
+  DUPLICATE_IMPLEMENTS_TYPE("Duplicate type in the implements clause"),
   DUPLICATE_INITIALIZATION("Duplicate initialization of '%s'"),
   DUPLICATE_FUNCTION_EXPRESSION("Duplicate function expression '%s'"),
   DUPLICATE_LABEL_IN_SWITCH_STATEMENT("Duplicate label in switch statement"),
   DUPLICATE_LOCAL_VARIABLE_ERROR("Duplicate local variable '%s'"),
   DUPLICATE_MEMBER("Duplicate member '%s'"),
   DUPLICATE_NAMED_ARGUMENT("Duplicate named parameter argument"),
   DUPLICATE_PARAMETER("Duplicate parameter '%s'"),
   DUPLICATE_TOP_LEVEL_DECLARATION("duplicate top-level declaration %s at %s"),
   DUPLICATE_TOP_LEVEL_DECLARATION_IMPORT("Duplicate import '%s' in %s prefix '%s' -  %s - %s"),
   DUPLICATE_TYPE_VARIABLE("Duplicate type variable '%s'"),
@@ skipping 138 matching lines @@
   @Override
   public SubSystem getSubSystem() {
     return SubSystem.RESOLVER;
   }
 
   @Override
   public boolean needsRecompilation() {
     return true;
   }
 }