Log unresolved URIs using 'logInformation', so don't send to IDE.

pkg/analyzer/lib/src/generated/source.dart

 // Copyright (c) 2014, 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.
 
 library engine.source;
 
 import 'dart:collection';
 import "dart:math" as math;
 
 import 'package:analyzer/file_system/file_system.dart';
@@ skipping 725 matching lines @@
     if (containedUri == null || containedUri.isEmpty) {
       return null;
     }
     try {
       // Force the creation of an escaped URI to deal with spaces, etc.
       return _internalResolveUri(
           containingSource, parseUriWithException(containedUri));
     } catch (exception, stackTrace) {
       String containingFullName =
           containingSource != null ? containingSource.fullName : '<null>';
-      AnalysisEngine.instance.logger.logError(
+      AnalysisEngine.instance.logger.logInformation(
           "Could not resolve URI ($containedUri) relative to source ($containingFullName)",
           new CaughtException(exception, stackTrace));
       return null;
     }
   }
 
   /**
    * Return an absolute URI that represents the given source, or `null` if a valid URI cannot
    * be computed.
    *
@@ skipping 320 matching lines @@
   Source resolveAbsolute(Uri uri, [Uri actualUri]);
 
   /**
    * Return an absolute URI that represents the given [source], or `null` if a
    * valid URI cannot be computed.
    *
    * The computation should be based solely on [source.fullName].
    */
   Uri restoreAbsolute(Source source) => null;
 }