[macros] Fix _checkForKernelRuntime.

The previous implementation always returns "true", making the PR a
no-op as it only does something for AOT runtimes. e2e test coverage
will land in
https://dart-review.googlesource.com/c/sdk/+/353100 to prevent such
mistakes in future.

R=johnniwinther@google.com

Change-Id: I8481187070a0af12a3f3bd77baa471f1a7d3256d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/355682
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Auto-Submit: Morgan :) <davidmorgan@google.com>
Commit-Queue: Morgan :) <davidmorgan@google.com>

pkg/_fe_analyzer_shared/lib/src/util/runtimes.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:isolate';
+import 'dart:typed_data';
 
 /// Whether the current runtime can register kernel blobs and launch kernel
 /// isolates.
@@ -11,10 +12,17 @@ bool get isKernelRuntime => _isKernelRuntime ??= _checkForKernelRuntime();
 bool? _isKernelRuntime;
 
 bool _checkForKernelRuntime() {
+  // `createUriForKernelBlob` throws `UnsupportedError` if kernel blobs are not
+  // supported at all. We don't actually want to register kernel so pass
+  // invalid kernel, an empty list, resulting in an `ArgumentError` if kernel
+  // blobs are supported.
   try {
-    (Isolate.current as dynamic).createUriForKernelBlob;
-    return true;
-  } catch (_) {
+    (Isolate.current as dynamic)
+        .createUriForKernelBlob(new Uint8List.fromList(const []));
+    throw new StateError('Expected failure.');
+  } on UnsupportedError {
     return false;
+  } on ArgumentError {
+    return true;
   }
 }

pkg/front_end/test/static_types/cfe_allowed.json

@@ -8,7 +8,7 @@
     "Dynamic invocation of 'split'.": 1
   },
   "pkg/_fe_analyzer_shared/lib/src/util/runtimes.dart": {
-    "Dynamic access of 'createUriForKernelBlob'.": 1
+    "Dynamic invocation of 'createUriForKernelBlob'.": 1
   },
   "pkg/front_end/lib/src/macros/isolate_macro_serializer.dart": {
     "Dynamic invocation of 'unregisterKernelBlobUri'.": 1,