Shard based on relative originTestPath

dart/tools/testing/dart/test_suite.dart

Index: dart/tools/testing/dart/test_suite.dart
diff --git a/dart/tools/testing/dart/test_suite.dart b/dart/tools/testing/dart/test_suite.dart
index 0b6904b50451117bbf0b3a123970f08b78962b45..aeb782b9bd7f4bf6bf4ead0f5d33efa37556ff10 100644
--- a/dart/tools/testing/dart/test_suite.dart
+++ b/dart/tools/testing/dart/test_suite.dart
@@ -273,11 +273,12 @@ abstract class TestSuite {
     int shards = configuration['shards'];
     if (shards > 1) {
       int shard = configuration['shard'];
-      if ("${testCase.info.originTestPath}".hashCode % shards != shard - 1) {
+      var testPath =
+          testCase.info.originTestPath.relativeTo(TestUtils.dartDir());
+      if ("$testPath".hashCode % shards != shard - 1) {
         return;
       }
     }
-
     // Test if the selector includes this test.
     RegExp pattern = configuration['selectors'][suiteName];
     if (!pattern.hasMatch(testCase.displayName)) {