Use URIs rather than paths in front end API.

pkg/front_end/tool/perf.dart

Index: pkg/front_end/tool/perf.dart
diff --git a/pkg/front_end/tool/perf.dart b/pkg/front_end/tool/perf.dart
index a69251bb81889a0a93b435c8c4232ca12d007e8d..7c4e4cd1d7be694a46ad8d0e3b88b95d3f8cd90e 100644
--- a/pkg/front_end/tool/perf.dart
+++ b/pkg/front_end/tool/perf.dart
@@ -115,15 +115,16 @@ Future<Program> generateKernel(Uri entryUri,
   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();