[kernel] Make fasta call a new constructor on FallThroughError

pkg/front_end/lib/src/fasta/target_implementation.dart

 // Copyright (c) 2016, 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.
 
 library fasta.target_implementation;
 
 import 'package:kernel/target/targets.dart' as backend show Target;
 
 import 'builder/builder.dart' show Builder, ClassBuilder, LibraryBuilder;
 
@@ skipping 69 matching lines @@
   /// accept a single argument which is the name of the field.
   Builder getDuplicatedFieldInitializerError(Loader loader) {
     if (cachedDuplicatedFieldInitializerError != null) {
       return cachedDuplicatedFieldInitializerError;
     }
     return cachedDuplicatedFieldInitializerError = loader.coreLibrary
         .getConstructor("_DuplicatedFieldInitializerError",
             bypassLibraryPrivacy: true);
   }
 
-  /// Returns a reference to the constructor of [FallThroughError] error.  The
-  /// constructor is expected to accept no arguments.
-  Builder getFallThroughError(Loader loader) {
-    if (cachedFallThroughError != null) {
-      return cachedFallThroughError;
-    }
-    return cachedFallThroughError =
-        loader.coreLibrary.getConstructor("FallThroughError");
-  }
-
   /// Returns a reference to the constructor used for creating `native`
   /// annotations. The constructor is expected to accept a single argument of
   /// type String, which is the name of the native method.
   Builder getNativeAnnotation(Loader loader) {
     if (cachedNativeAnnotation != null) return cachedNativeAnnotation;
     LibraryBuilder internal = loader.read(Uri.parse("dart:_internal"), -1);
     return cachedNativeAnnotation = internal.getConstructor("ExternalName");
   }
 
   void loadExtraRequiredLibraries(Loader loader) {
@@ skipping 27 matching lines @@
   void readPatchFiles(LibraryBuilder library) {
     assert(library.uri.scheme == "dart");
     List<Uri> patches = uriTranslator.patches[library.uri.path];
     if (patches != null) {
       for (Uri patch in patches) {
         library.loader.read(patch, -1, fileUri: patch, isPatch: true);
       }
     }
   }
 }