[test_runner] Use sound null safety js files

The bootstrapping was still loading the wrong version of the sdk and
pre-compiled packages when running tests for DDC.

Update constant_null_safety_mode_test to test a constant that is
defined within the sdk itself in addition to one defined in the test.

Change-Id: I8938ed92d866cfca0ce42567f03bed5f3dd9f10c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/154121
Reviewed-by: Bob Nystrom <rnystrom@google.com>
Commit-Queue: Nicholas Shahan <nshahan@google.com>

Author: nshahan

pkg/test_runner/lib/src/browser.dart

@@ -152,11 +152,10 @@ String dartdevcHtml(String testName, String testNameAlias, String testJSDir,
     Compiler compiler, NnbdMode mode, bool nonNullAsserts) {
   var testId = pathToJSIdentifier(testName);
   var testIdAlias = pathToJSIdentifier(testNameAlias);
-  var isKernel = compiler == Compiler.dartdevk;
   var isNnbd = mode != NnbdMode.legacy;
   var isNnbdStrong = mode == NnbdMode.strong;
-  var sdkPath = isKernel ? 'kernel/amd/dart_sdk' : 'js/amd/dart_sdk';
-  var pkgDir = isKernel ? 'pkg_kernel' : 'pkg';
+  var sdkPath = isNnbdStrong ? 'sound/amd/dart_sdk' : 'kernel/amd/dart_sdk';
+  var pkgDir = isNnbdStrong ? 'pkg_sound' : 'pkg_kernel';
   var packagePaths = testPackages
       .map((p) => '    "$p": "/root_build/gen/utils/dartdevc/$pkgDir/$p",')
       .join("\n");

tests/language/nnbd/constant_null_safety_mode_test.dart

@@ -7,4 +7,18 @@ import 'package:expect/expect.dart';
 main() {
   const trueInWeakMode = <Null>[] is List<int>;
   Expect.equals(isWeakMode, trueInWeakMode);
+
+  // The following tests use the Uri.pathSegments() to access a constant list
+  // that is defined in the SDK and verify the type associated with it does not
+  // allow null when running with sound null safety.
+  var emptyUri = Uri(pathSegments: []);
+  dynamic stringList = emptyUri.pathSegments.toList();
+  if (isStrongMode) {
+    Expect.throwsTypeError(() {
+      stringList.add(null);
+    });
+  } else {
+    stringList.add(null);
+    Expect.listEquals([null], stringList);
+  }
 }