[vm/bytecode] Fix handling of contravariant parameters in isUncheckedCall

Fixes language_2/variance/variance_in_method_test.dart when bytecode is
enabled in AOT mode.

Change-Id: I2d1338f2d68ab3a91127cdbeb60c71597d4da718
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/127981
Reviewed-by: Régis Crelier <regis@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>

pkg/vm/lib/bytecode/generics.dart

@@ -226,14 +226,31 @@ bool isUncheckedCall(Member interfaceTarget, Expression receiver,
 
   DartType receiverStaticType = getStaticType(receiver, staticTypeContext);
   if (receiverStaticType is InterfaceType) {
-    if (receiverStaticType.typeArguments.isEmpty) {
+    final typeArguments = receiverStaticType.typeArguments;
+    if (typeArguments.isEmpty) {
       return true;
     }
 
-    if (receiverStaticType.typeArguments.every(
-        (t) => isSealedType(t, staticTypeContext.typeEnvironment.coreTypes))) {
-      return true;
+    final typeParameters = receiverStaticType.classNode.typeParameters;
+    assert(typeArguments.length == typeParameters.length);
+    for (int i = 0; i < typeArguments.length; ++i) {
+      switch (typeParameters[i].variance) {
+        case Variance.covariant:
+          if (!isSealedType(
+              typeArguments[i], staticTypeContext.typeEnvironment.coreTypes)) {
+            return false;
+          }
+          break;
+        case Variance.invariant:
+          break;
+        case Variance.contravariant:
+          return false;
+        default:
+          throw 'Unexpected variance ${typeParameters[i].variance} of '
+              '${typeParameters[i]} in ${receiverStaticType.classNode}';
+      }
     }
+    return true;
   }
   return false;
 }

pkg/vm/tool/precompiler2

@@ -25,7 +25,8 @@ for arg in "$@"; do
     --packages=*)
     PACKAGES="$arg"
     ;;
-    --enable-asserts)
+    --enable-asserts | \
+    --enable-experiment=*)
     GEN_KERNEL_OPTIONS+=("$arg")
     OPTIONS+=("$arg")
     ;;