Support runtime check of function types.

sdk/lib/_internal/compiler/implementation/ssa/optimize.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of ssa;
 
 abstract class OptimizationPhase {
   String get name;
   void visitGraph(HGraph graph);
 }
@@ skipping 588 matching lines @@
     }
     return node;
   }
 
   HInstruction visitTypeConversion(HTypeConversion node) {
     HInstruction value = node.inputs[0];
     DartType type = node.typeExpression;
     if (type != null && (!type.isRaw || type.kind == TypeKind.TYPE_VARIABLE)) {
       return node;
     }
+    if (type != null && type.kind == TypeKind.FUNCTION) {
+      // TODO(johnniwinther): Optimize function type conversions.
+      return node;
+    }
     HType convertedType = node.instructionType;
     if (convertedType.isUnknown()) return node;
     HType combinedType = value.instructionType.intersection(
         convertedType, compiler);
     return (combinedType == value.instructionType) ? value : node;
   }
 
   Element findConcreteFieldForDynamicAccess(HInstruction receiver,
                                             Selector selector) {
     HType receiverType = receiver.instructionType;
@@ skipping 868 matching lines @@
     }
 
     // For other fields having setters in the generative constructor body, set
     // the type to UNKNOWN to avoid relying on the type set in the initializer
     // list.
     allSetters.forEach((Element element) {
       backend.registerFieldConstructor(element, HType.UNKNOWN);
     });
   }
 }