[gardening] Replace exitCode 0 expects in dartdev native_assets tests.

nativeAssetsTest takes a named argument expectExitCodeZero which,
if true, checks to see if the exit code is 0 and if not, prints
both stdout and stderr before using an expect to stop the test.

Fix tests that pass false for expectExitCodeZero and then manually
expect an exit code of 0 without printing stdout/stderr to pass true for
that argument.

TEST=pkg/dartdev/test/native_assets/build_test
     pkg/dartdev/test/native_assets/run_test

Change-Id: Id0a52e1df1b0260cf9014812ac8c1dee9c91a8e0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/385921
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>
diff --git a/pkg/dartdev/test/native_assets/build_test.dart b/pkg/dartdev/test/native_assets/build_test.dart
index ec0ad72..219f59e 100644
--- a/pkg/dartdev/test/native_assets/build_test.dart
+++ b/pkg/dartdev/test/native_assets/build_test.dart
@@ -152,7 +152,7 @@
 
   test('dart link assets', timeout: longTimeout, () async {
     await nativeAssetsTest('drop_dylib_link', (dartAppUri) async {
-      final result = await runDart(
+      await runDart(
         arguments: [
           '--enable-experiment=native-assets',
           'build',
@@ -160,9 +160,8 @@
         ],
         workingDirectory: dartAppUri,
         logger: logger,
-        expectExitCodeZero: false,
+        expectExitCodeZero: true,
       );
-      expect(result.exitCode, 0);
 
       // Check that the build directory exists
       final directory =
diff --git a/pkg/dartdev/test/native_assets/run_test.dart b/pkg/dartdev/test/native_assets/run_test.dart
index fb043c4..09cf606d 100644
--- a/pkg/dartdev/test/native_assets/run_test.dart
+++ b/pkg/dartdev/test/native_assets/run_test.dart
@@ -94,7 +94,7 @@
 
   test('dart link assets succeeds', timeout: longTimeout, () async {
     await nativeAssetsTest('drop_dylib_link', (dartAppUri) async {
-      final result = await runDart(
+      await runDart(
         arguments: [
           '--enable-experiment=native-assets',
           'run',
@@ -103,9 +103,8 @@
         ],
         workingDirectory: dartAppUri,
         logger: logger,
-        expectExitCodeZero: false,
+        expectExitCodeZero: true,
       );
-      expect(result.exitCode, 0);
     });
   });