Store Typedef(s) in kernel when parsing with Fasta, deserilize in DillLibraryBuilder.

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

Index: pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
index 64739bd3bd31e72328d700e019bdab7a6a2134b7..6da04480c7836d046c83a2e7d9f4b67057ca2888 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
@@ -652,9 +652,8 @@ class KernelLibraryBuilder
       library.addMember(builder.build(this)..isStatic = true);
     } else if (builder is KernelProcedureBuilder) {
       library.addMember(builder.build(this)..isStatic = true);
-    } else if (builder is FunctionTypeAliasBuilder) {
-      // Kernel discard typedefs and use their corresponding function types
-      // directly.
+    } else if (builder is KernelFunctionTypeAliasBuilder) {
+      library.addTypedef(builder.build(this));
     } else if (builder is KernelEnumBuilder) {
       library.addClass(builder.build(this, coreLibrary));
     } else if (builder is PrefixBuilder) {