[test_runner]: provide package_config.json by default.

As we intend to remove the '.packages' file in the SDK, the test runner
should no longer use it as a default value for the '--packages' flag.

Change-Id: Iaaa16a974f8fc137e6f779494903859a242d7f9c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/243643
Commit-Queue: Jonas Termansen <sortie@google.com>
Reviewed-by: Jonas Termansen <sortie@google.com>
Auto-Submit: Sigmund Cherem <sigmund@google.com>
diff --git a/pkg/test_runner/lib/src/configuration.dart b/pkg/test_runner/lib/src/configuration.dart
index d68d39c..92cf4a9 100644
--- a/pkg/test_runner/lib/src/configuration.dart
+++ b/pkg/test_runner/lib/src/configuration.dart
@@ -172,7 +172,8 @@
 
   String get packages {
     // If the .packages file path wasn't given, find it.
-    _packages ??= Repository.uri.resolve('.packages').toFilePath();
+    _packages ??=
+        Repository.uri.resolve('.dart_tool/package_config.json').toFilePath();
 
     return _packages;
   }
diff --git a/pkg/test_runner/lib/src/test_suite.dart b/pkg/test_runner/lib/src/test_suite.dart
index faf6d57..818acd7 100644
--- a/pkg/test_runner/lib/src/test_suite.dart
+++ b/pkg/test_runner/lib/src/test_suite.dart
@@ -925,11 +925,7 @@
             _createUrlPathFromFile(Path('$compilationTempDir/$nameNoExt.js'));
         content = dart2jsHtml(testFile.path.toNativePath(), scriptPath);
       } else {
-        var packageRoot = packagesArgument(configuration.packages);
-        packageRoot =
-            packageRoot == null ? nameNoExt : packageRoot.split("=").last;
-        var nameFromModuleRoot =
-            testFile.path.relativeTo(Path(packageRoot).directoryPath);
+        var nameFromModuleRoot = testFile.path.relativeTo(Repository.dir);
         var nameFromModuleRootNoExt =
             "${nameFromModuleRoot.directoryPath}/$nameNoExt";
         var jsDir =
diff --git a/pkg/test_runner/lib/src/testing_servers.dart b/pkg/test_runner/lib/src/testing_servers.dart
index ac04529..0a6814b 100644
--- a/pkg/test_runner/lib/src/testing_servers.dart
+++ b/pkg/test_runner/lib/src/testing_servers.dart
@@ -91,7 +91,7 @@
         ? Repository.uri
         : Uri.base.resolveUri(Uri.directory(dartDirectory));
     var packagesUri = packages == null
-        ? dartDirectoryUri.resolve('.packages')
+        ? dartDirectoryUri.resolve('.dart_tool/package_config.json')
         : Uri.file(packages);
     return TestingServers._(useContentSecurityPolicy, buildDirectoryUri,
         dartDirectoryUri, packagesUri, runtime);