Use URIs rather than paths in front end API.

pkg/front_end/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 front_end and measure its performance.
 library front_end.tool.perf;
 
 import 'dart:async';
 import 'dart:io' show exit;
 
@@ skipping 97 matching lines @@
     {bool useSdkSummary: false, bool compileSdk: true}) async {
   // TODO(sigmund): this is here only to compute the input size,
   // we should extract the input size from the frontend instead.
   scanReachableFiles(entryUri);
 
   var dartkTimer = new Stopwatch()..start();
   // TODO(sigmund): add a constructor with named args to compiler options.
   var options = new CompilerOptions()
     ..strongMode = false
     ..compileSdk = compileSdk
-    ..packagesFilePath = '.packages'
+    ..packagesFileUri = new Uri.file('.packages')

[Siggi Cherem (dart-lang), 2017/01/11 22:59:53]

probably doesn't matter, but another option here would be to make it absolute
right away by doing `Uri.base.resolve('relative-path')`.

[Paul Berry, 2017/01/12 23:10:04]

One of the goals of the FileSystem abstraction is to make it unnecessary for
client code to deal with stuff like converting paths to absolute.  So I'd prefer
to leave it as is.

     ..onError = ((e) => print('${e.message}'));
   if (useSdkSummary) {
     // TODO(sigmund): adjust path based on the benchmark runner architecture.
     // Possibly let the runner make the file available at an architecture
     // independent location.
-    options.sdkSummary = 'out/ReleaseX64/dart-sdk/lib/_internal/spec.sum';
+    options.sdkSummary =
+        new Uri.file('out/ReleaseX64/dart-sdk/lib/_internal/spec.sum');
   } else {
-    options.sdkPath = 'sdk';
+    options.sdkRoot = new Uri.file('sdk');
   }
   Program program = await kernelForProgram(entryUri, options);
   dartkTimer.stop();
   var suffix = useSdkSummary ? '_sum' : '';
   report('kernel_gen_e2e${suffix}', dartkTimer.elapsedMicroseconds);
   return program;
 }
 
 /// Generates unlinkmed summaries for all files in [files], and returns them in
 /// an [_UnlinkedSummaries] container.
@@ skipping 202 matching lines @@
 class _Scanner extends Scanner {
   _Scanner(String contents) : super(new CharSequenceReader(contents)) {
     preserveComments = false;
   }
 
   @override
   void reportError(errorCode, int offset, List<Object> arguments) {
     // ignore errors.
   }
 }