[vm/shared] Ensure shared initial field table is used with shared fields.

Fixes flutter/flutter#170038
TEST=shared_static_final_test

Change-Id: Ia242b5d9c661782e5a6018ba96211a75cc47c1a3
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/436200
Reviewed-by: Slava Egorov <[email protected]>
Commit-Queue: Alexander Aprelev <[email protected]>

Author: aam

runtime/tests/vm/dart/shared_static_final_test.dart

@@ -0,0 +1,14 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+//
+// VMOptions=--experimental-shared-data
+//
+import 'package:expect/expect.dart';
+
+@pragma('vm:shared')
+final int foo = 42;
+
+main() {
+  Expect.equals(42, foo);
+}

runtime/vm/object.cc

@@ -13085,11 +13085,12 @@ ObjectPtr Field::StaticConstFieldValue() const {
 
   auto thread = Thread::Current();
   auto zone = thread->zone();
-  auto initial_field_table = thread->isolate_group()->initial_field_table();
+  auto initial_field_table =
+      is_shared() ? thread->isolate_group()->shared_initial_field_table()
+                  : thread->isolate_group()->initial_field_table();
 
   // We can safely cache the value of the static const field in the initial
   // field table.
-  ASSERT(!is_shared());
   auto& value = Object::Handle(
       zone, initial_field_table->At(field_id(), /*concurrent_use=*/true));
   if (value.ptr() == Object::sentinel().ptr()) {
@@ -13111,9 +13112,10 @@ ObjectPtr Field::StaticConstFieldValue() const {
 void Field::SetStaticConstFieldValue(const Instance& value,
                                      bool assert_initializing_store) const {
   ASSERT(is_static());
-  ASSERT(!is_shared());
   auto thread = Thread::Current();
-  auto initial_field_table = thread->isolate_group()->initial_field_table();
+  auto initial_field_table =
+      is_shared() ? thread->isolate_group()->shared_initial_field_table()
+                  : thread->isolate_group()->initial_field_table();
 
   SafepointWriteRwLocker ml(thread, thread->isolate_group()->program_lock());
   ASSERT(initial_field_table->At(field_id()) == Object::sentinel().ptr() ||