Fix warnings in dart2js and analyzer caused by Fasta.

pkg/compiler/lib/src/source_file_provider.dart

Index: pkg/compiler/lib/src/source_file_provider.dart
diff --git a/pkg/compiler/lib/src/source_file_provider.dart b/pkg/compiler/lib/src/source_file_provider.dart
index 80275161ec5fd42b1d33acc01fec5c703b1eca5f..eca1c62bf3b3b72cf0b89f262db10c57402dbf46 100644
--- a/pkg/compiler/lib/src/source_file_provider.dart
+++ b/pkg/compiler/lib/src/source_file_provider.dart
@@ -88,7 +88,9 @@ abstract class SourceFileProvider implements CompilerInput {
 
   // TODO(johnniwinther): Remove this when no longer needed for the old compiler
   // API.
-  Future/*<List<int> | String>*/ call(Uri resourceUri) => throw "unimplemented";
+  Future /* <List<int> | String> */ call(Uri resourceUri) {
+    throw "unimplemented";
+  }
 
   relativizeUri(Uri uri) => relativize(cwd, uri, isWindows);