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

pkg/analyzer/lib/src/fasta/mock_element.dart

Index: pkg/analyzer/lib/src/fasta/mock_element.dart
diff --git a/pkg/analyzer/lib/src/fasta/mock_element.dart b/pkg/analyzer/lib/src/fasta/mock_element.dart
index f4404ae775c59553c7519edd9ac8bd43e4ba7fb8..c55c6279dc6179563a0940bde6b4b370c569383f 100644
--- a/pkg/analyzer/lib/src/fasta/mock_element.dart
+++ b/pkg/analyzer/lib/src/fasta/mock_element.dart
@@ -347,6 +347,17 @@ abstract class MockFunctionElement extends MockElement
   FunctionDeclaration computeNode() => internalError("not supported.");
 }
 
+abstract class MockFunctionTypeAliasElement extends MockElement
+    implements FunctionTypeAliasElement {
+  MockFunctionTypeAliasElement() : super(ElementKind.FUNCTION_TYPE_ALIAS);
+
+  CompilationUnitElement get enclosingElement {
+    return internalError("not supported.");
+  }
+
+  TypeAlias computeNode() => internalError("not supported.");
+}
+
 abstract class MockParameterElement extends MockElement
     implements ParameterElement {
   MockParameterElement() : super(ElementKind.PARAMETER);