Set fileUri when creating library builders.

pkg/front_end/lib/src/fasta/source/source_loader.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.
 
 library fasta.source_loader;
 
 import 'dart:async' show
     Future;
 
 import 'dart:io' show
@@ skipping 61 matching lines @@
   CoreTypes coreTypes;
 
   // Used when building analyzer ASTs.
   ElementStore elementStore;
 
   SourceLoader(TargetImplementation target)
       : super(target);
 
   Future<Token> tokenize(SourceLibraryBuilder library,
       {bool suppressLexicalErrors: false}) async {
-    Uri uri = library.fileUri ?? library.uri;
-    if (uri.scheme != "file") {
-      uri = target.translateUri(uri);
-      if (uri == null) {
-        print("Skipping ${library.uri}");
-        return null;
-      }
-      library.fileUri = uri;
+    Uri uri = library.fileUri;
+    if (uri == null || uri.scheme != "file") {
+      return inputError(library.uri, -1, "Not found: ${library.uri}.");
     }
     try {
       List<int> bytes = await readBytesFromFile(uri);
       byteCount += bytes.length - 1;
       Token token = scan(bytes).tokens;
       while (token is ErrorToken) {
         if (!suppressLexicalErrors) {
           ErrorToken error = token;
           String message = new InputError(
               uri, token.charOffset, error.assertionMessage).format();
@@ skipping 251 matching lines @@
     ticker.logMs("Built analyzer element model.");
   }
 
   void computeHierarchy(Program program) {
     hierarchy = new ClassHierarchy(program);
     ticker.logMs("Computed class hierarchy");
     coreTypes = new CoreTypes(program);
     ticker.logMs("Computed core types");
   }
 }