Fix perf_test.

pkg/compiler/tool/perf.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.
 
 /// An entrypoint used to run portions of dart2js and measure its performance.
 library compiler.tool.perf;
 
 import 'dart:async';
 import 'dart:io';
 
@@ skipping 276 matching lines @@
     Uri resourceUri = _translateUri(uri);
     if (resourceUri == null || resourceUri.scheme == 'dart-ext') {
       throw '$uri not resolved or unsupported.';
     }
     var file = _cache[resourceUri];
     if (file != null) return _cache[resourceUri];
     return _cache[resourceUri] = await _readFile(resourceUri);
   }
 
   Future<SourceFile> _readFile(Uri uri) async {
-    var data = await inputProvider.readFromUri(uri);
-    if (data is List<int>) return new Utf8BytesSourceFile(uri, data);
-    if (data is String) return new StringSourceFile.fromUri(uri, data);
-    // TODO(sigmund): properly handle errors, just report, return null, wrap
-    // above and continue...
-    throw "Expected a 'String' or a 'List<int>' from the input "
-        "provider, but got: ${data.runtimeType}.";
+    return await inputProvider.readFromUri(uri, inputKind: InputKind.utf8);
   }
 
   Uri _translateUri(Uri uri) {
     if (uri.scheme == 'dart') return sdkLibraries[uri.path];
     if (uri.scheme == 'package') return _translatePackageUri(uri);
     return uri;
   }
 
   Uri _translatePackageUri(Uri uri) {
     checkValidPackageUri(uri);
@@ skipping 68 matching lines @@
           print('compilation failed!');
           exit(1);
         }
 
         backend.onResolutionEnd();
         closeResolution();
         var program = (backend as dynamic).kernelTask.program;
         print('total libraries: ${program.libraries.length}');
       });
 }