Catch Uri.parse() FormatException and skip the URI.

pkg/analyzer/lib/src/dart/analysis/file_state.dart

 // Copyright (c) 2016, 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.
 
 import 'dart:convert';
 import 'dart:typed_data';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/error/listener.dart';
@@ skipping 471 matching lines @@
     }
 
     // Return whether the API signature changed.
     return apiSignatureChanged;
   }
 
   @override
   String toString() => path;
 
   /**
    * Return the [FileState] for the given [relativeUri].

[Brian Wilkerson, 2017/01/31 21:51:23]

Maybe mention that `null` is an expected result.

    */
   FileState _fileForRelativeUri(String relativeUri) {
-    Uri absoluteUri = resolveRelativeUri(uri, Uri.parse(relativeUri));
+    Uri absoluteUri;
+    try {
+      absoluteUri = resolveRelativeUri(uri, Uri.parse(relativeUri));
+    } on FormatException catch (e) {
+      return null;
+    }
     return _fsState.getFileForUri(absoluteUri);
   }
 
   /**
    * Return `true` if the given byte lists are equal.
    */
   static bool _equalByteLists(List<int> a, List<int> b) {
     if (a == null) {
       return b == null;
     } else if (b == null) {
@@ skipping 199 matching lines @@
         .where((f) => f._transitiveFiles == null)
         .toSet();
   }
 
   Set<FileState> get filesWithoutTransitiveSignature {
     return state._uriToFile.values
         .where((f) => f._transitiveSignature == null)
         .toSet();
   }
 }