Remove hack from KernelTypeInferrer.inferInitializer.

pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart

 // Copyright (c) 2017, 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.
 
 /// This file declares a "shadow hierarchy" of concrete classes which extend
 /// the kernel class hierarchy, adding methods and fields needed by the
 /// BodyBuilder.
 ///
 /// Instances of these classes may be created using the factory methods in
 /// `ast_factory.dart`.
@@ skipping 2173 matching lines @@
 
   @override
   DartType inferFieldTopLevel(
       KernelField field, DartType type, bool typeNeeded) {
     if (field.initializer == null) return const DynamicType();
     return inferExpression(field.initializer, type, typeNeeded);
   }
 
   @override
   void inferInitializer(Initializer initializer) {
-    if (initializer is KernelInitializer) {
-      // Use polymorphic dispatch on [KernelInitializer] to perform whatever
-      // kind of type inference is correct for this kind of initializer.
-      // TODO(paulberry): experiment to see if dynamic dispatch would be better,
-      // so that the type hierarchy will be simpler (which may speed up "is"
-      // checks).
-      return initializer._inferInitializer(this);
-    } else {
-      // Encountered an initializer type for which type inference is not yet
-      // implemented, so just skip it for now.
-      // TODO(paulberry): once the BodyBuilder uses shadow classes for
-      // everything, this case should no longer be needed.
-    }
+    assert(initializer is KernelInitializer);
+    // Use polymorphic dispatch on [KernelInitializer] to perform whatever
+    // kind of type inference is correct for this kind of initializer.
+    // TODO(paulberry): experiment to see if dynamic dispatch would be better,
+    // so that the type hierarchy will be simpler (which may speed up "is"
+    // checks).
+    KernelInitializer kernelInitializer = initializer;
+    return kernelInitializer._inferInitializer(this);
   }
 
   @override
   void inferStatement(Statement statement) {
     if (statement is KernelStatement) {
       // Use polymorphic dispatch on [KernelStatement] to perform whatever kind
       // of type inference is correct for this kind of statement.
       // TODO(paulberry): experiment to see if dynamic dispatch would be better,
       // so that the type hierarchy will be simpler (which may speed up "is"
       // checks).
@@ skipping 258 matching lines @@
   accept(v) => unsupported("accept", -1, null);
 
   accept1(v, arg) => unsupported("accept1", -1, null);
 
   getStaticType(types) => unsupported("getStaticType", -1, null);
 
   transformChildren(v) => unsupported("transformChildren", -1, null);
 
   visitChildren(v) => unsupported("visitChildren", -1, null);
 }