Add no-op entry point for IncrementalCompiler

Change-Id: Ibe1fef376d1576554b85a2debcde2c3b19c21d92
Reviewed-on: https://dart-review.googlesource.com/60425
Reviewed-by: Jens Johansen <jensj@google.com>
Commit-Queue: Peter von der Ahé <ahe@google.com>
diff --git a/pkg/front_end/tool/_fasta/entry_points.dart b/pkg/front_end/tool/_fasta/entry_points.dart
index 3af6703..2c27df0 100644
--- a/pkg/front_end/tool/_fasta/entry_points.dart
+++ b/pkg/front_end/tool/_fasta/entry_points.dart
@@ -26,6 +26,9 @@
 
 import 'package:front_end/src/fasta/dill/dill_target.dart' show DillTarget;
 
+import 'package:front_end/src/fasta/incremental_compiler.dart'
+    show IncrementalCompiler;
+
 import 'package:front_end/src/fasta/kernel/kernel_target.dart'
     show KernelTarget;
 
@@ -161,6 +164,16 @@
   }
 }
 
+incrementalEntryPoint(List<String> arguments) async {
+  installAdditionalTargets();
+  await withGlobalOptions("incremental", arguments, true,
+      (CompilerContext c, _) {
+    // TODO(ahe): Extend this entry point so it can replace
+    // batchEntryPoint.
+    new IncrementalCompiler(c);
+  });
+}
+
 Future<KernelTarget> outline(List<String> arguments) async {
   try {
     return await withGlobalOptions("outline", arguments, true,