Report error on parsing URI cleanly (don't throw exception)

compiler/java/com/google/dart/compiler/DartCompilerErrorCode.java

 // 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.
 
 package com.google.dart.compiler;
 
 /**
  * Valid error codes for the errors produced by the Dart compiler.
  */
 public enum DartCompilerErrorCode implements ErrorCode {
+  COULD_NOT_PARSE_IMPORT("Could not parse import: %s"),
   ENTRY_POINT_METHOD_CANNOT_HAVE_PARAMETERS("Main entry point method cannot have parameters"),
   ENTRY_POINT_METHOD_MAY_NOT_BE_GETTER("Entry point \"%s\" may not be a getter"),
   ENTRY_POINT_METHOD_MAY_NOT_BE_SETTER("Entry point \"%s\" may not be a setter"),
   ILLEGAL_DIRECTIVES_IN_SOURCED_UNIT("A source which was included by another source via a "
       + "#source directive cannot itself contain directives: %s"),
   IO("Input/Output error: %s"),
   MISSING_LIBRARY_DIRECTIVE("a library which is imported is missing a #library directive: %s"),
   MISSING_SOURCE("Cannot find referenced source: %s"),
   NO_ENTRY_POINT("No entrypoint specified for app");
   private final ErrorSeverity severity;
   private final String message;
 
   /**
    * Initialize a newly created error code to have the given message and ERROR severity.
    */
   private DartCompilerErrorCode(String message) {
     this(ErrorSeverity.ERROR, message);
   }
 
   /**
    * Initialize a newly created error code to have the given severity and message.
    */
   private DartCompilerErrorCode(ErrorSeverity severity, String message) {
     this.severity = severity;
     this.message = message;
   }
 
+  @Override
   public String getMessage() {
     return message;
   }
 
+  @Override
   public ErrorSeverity getErrorSeverity() {
     return severity;
   }
 
+  @Override
   public SubSystem getSubSystem() {
     return SubSystem.COMPILER;
   }
 }