Change dart:io Platform.script to return a Uri.

pkg/analyzer/lib/src/services/runtime/coverage/coverage_impl.dart

Index: pkg/analyzer/lib/src/services/runtime/coverage/coverage_impl.dart
diff --git a/pkg/analyzer/lib/src/services/runtime/coverage/coverage_impl.dart b/pkg/analyzer/lib/src/services/runtime/coverage/coverage_impl.dart
index 3515fe2ced8a98ff6c8d987df3f848845c938e31..8e2fb90187588434f3917a91fefb11bf5a5aef58 100644
--- a/pkg/analyzer/lib/src/services/runtime/coverage/coverage_impl.dart
+++ b/pkg/analyzer/lib/src/services/runtime/coverage/coverage_impl.dart
@@ -190,7 +190,7 @@ class CoverageServer extends RewriteServer {
   String rewritePathContent(String path) {
     if (path.endsWith('__coverage_lib.dart')) {
       String implPath = pathos.joinAll([
-          pathos.dirname(Platform.script),
+          pathos.dirname(Platform.script.toFilePath()),
           '..', 'lib', 'src', 'services', 'runtime', 'coverage',
           'coverage_lib.dart']);
       var content = new File(implPath).readAsStringSync();