[dart2js] Fix DictionaryTypeMask hashCode and == consistency.

The serializer uses these to cache instances of DictionaryTypeMask for indexing. If these produce inconsistent results we can end up with different caching patterns leading to different serialized outputs.

Change-Id: I8550f6fc1cb2bb32a68b3274e6add2e7ee56930d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/403483
Auto-Submit: Nate Biggs <[email protected]>
Reviewed-by: Mayank Patke <[email protected]>
Commit-Queue: Mayank Patke <[email protected]>

Author: natebiggs

pkg/compiler/lib/src/inferrer/typemasks/dictionary_type_mask.dart

@@ -144,14 +144,14 @@ class DictionaryTypeMask extends MapTypeMask {
     if (identical(this, other)) return true;
     if (other is! DictionaryTypeMask) return false;
     return super == other &&
-        _typeMap.keys.every((k) => other._typeMap.containsKey(k)) &&
-        other._typeMap.keys.every(
-          (k) => _typeMap.containsKey(k) && _typeMap[k] == other._typeMap[k],
-        );
+        const MapEquality<String, TypeMask>().equals(_typeMap, other._typeMap);
   }
 
   @override
-  int get hashCode => Hashing.objectHash(_typeMap, super.hashCode);
+  int get hashCode => Hashing.mixHashCodeBits(
+    super.hashCode,
+    const MapEquality<String, TypeMask>().hash(_typeMap),
+  );
 
   @override
   String toString() {

pkg/compiler/lib/src/inferrer/typemasks/masks.dart

@@ -4,6 +4,7 @@
 
 library;
 
+import 'package:collection/collection.dart';
 import 'package:js_shared/variance.dart';
 import 'package:kernel/ast.dart' as ir;
 
@@ -141,7 +142,6 @@ class CommonMasks with AbstractValueDomain {
     _closedWorld,
   );
 
-  @override
   // TODO(50701): Use:
   //
   //     TypeMask.nonNullSubtype(commonElements.recordClass, _closedWorld);
@@ -150,8 +150,8 @@ class CommonMasks with AbstractValueDomain {
   // subtypes of Record or (2) several live subtypes of Record. Everything
   // 'works' for the similar interface `Function` because there are multiple
   // live subclasses of `Closure`.
-  late final TypeMask
-  recordType = nonNullType;
+  @override
+  late final TypeMask recordType = nonNullType;
 
   @override
   late final TypeMask listType = TypeMask.nonNullSubtype(