Incremental compiler: support optional arguments.

dart/pkg/compiler/lib/src/enqueue.dart

Index: dart/pkg/compiler/lib/src/enqueue.dart
diff --git a/dart/pkg/compiler/lib/src/enqueue.dart b/dart/pkg/compiler/lib/src/enqueue.dart
index fb8c2cf4de33360c1b681b1dc058716d8f147fc8..c2638b43a5d7c4614ad18ad30d4e461e8a36882c 100644
--- a/dart/pkg/compiler/lib/src/enqueue.dart
+++ b/dart/pkg/compiler/lib/src/enqueue.dart
@@ -812,10 +812,13 @@ class CodegenEnqueuer extends Enqueuer {
 
   final Set<Element> newlyEnqueuedElements;
 
+  final Set<Selector> newlySeenSelectors;
+
   CodegenEnqueuer(Compiler compiler,
                   ItemCompilationContext itemCompilationContextCreator())
       : queue = new Queue<CodegenWorkItem>(),
         newlyEnqueuedElements = compiler.cacheStrategy.newSet(),
+        newlySeenSelectors = compiler.cacheStrategy.newSet(),
         super('codegen enqueuer', compiler, itemCompilationContextCreator);
 
   bool isProcessed(Element member) =>
@@ -875,6 +878,13 @@ class CodegenEnqueuer extends Enqueuer {
       }
     }
   }
+
+  void handleUnseenSelector(String methodName, Selector selector) {
+    if (compiler.hasIncrementalSupport) {
+      newlySeenSelectors.add(selector);
+    }
+    super.handleUnseenSelector(methodName, selector);
+  }
 }
 
 /// Parameterizes filtering of which work items are enqueued.