Use `Function` as function type syntax.

pkg/compiler/lib/src/compiler.dart

Index: pkg/compiler/lib/src/compiler.dart
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index 536a2794bbbb4aab262ea5c37792bdea108da24f..db0841eb22b1ee26a96535af968d15651b6a5fdd 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -80,10 +80,10 @@ import 'universe/world_impact.dart' show ImpactStrategy, WorldImpact;
 import 'util/util.dart' show Link, Setlet;
 import 'world.dart' show ClosedWorld, ClosedWorldRefiner, OpenWorld, WorldImpl;
 
-typedef Backend MakeBackendFuncion(Compiler compiler);
+typedef MakeBackendFuncion = Backend Function(Compiler compiler);
 
-typedef CompilerDiagnosticReporter MakeReporterFunction(
-    Compiler compiler, CompilerOptions options);
+typedef MakeReporterFunction =
+    CompilerDiagnosticReporter Function(Compiler compiler, CompilerOptions options);
 
 abstract class Compiler implements LibraryLoaderListener {
   Measurer get measurer;