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 578 matching lines @@
       } else if (expressionMask.intersection(typeMask, compiler).isEmpty) {
         return graph.addConstantBool(false, compiler);
       }
     }
     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) {
+      if (!type.isRaw || type.kind == TypeKind.TYPE_VARIABLE) {
+        return node;
+      }
+      if (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) {
@@ skipping 719 matching lines @@
       // that knows it is not of a specific Type.
     }
 
     for (HIf ifUser in notIfUsers) {
       changeUsesDominatedBy(ifUser.elseBlock, input, convertedType);
       // TODO(ngeoffray): Also change uses for the then block on a HType
       // that knows it is not of a specific Type.
     }
   }
 }