Use predicates to check simple function types.

sdk/lib/_internal/compiler/implementation/js_backend/emitter.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 js_backend;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 2158 matching lines @@
       FunctionType methodType,
       Map<FunctionType, bool> functionTypeChecks,
       FunctionTypeSignatureEmitter emitFunctionTypeSignature,
       FunctionTypeTestEmitter emitIsFunctionTypeTest) {
     bool hasDynamicFunctionTypeCheck = false;
     int neededPredicates = 0;
     functionTypeChecks.forEach((FunctionType functionType, bool knownSubtype) {
       if (!knownSubtype) {
         registerDynamicFunctionTypeCheck(functionType);
         hasDynamicFunctionTypeCheck = true;
-      } else {
+      } else if (!backend.rti.isSimpleFunctionType(functionType)) {
+        // Simple function types are always checked using predicates and should
+        // not provoke generation of signatures.
         neededPredicates++;
       }
     });
     bool alwaysUseSignature = false;
     if (hasDynamicFunctionTypeCheck ||
         neededPredicates > MAX_FUNCTION_TYPE_PREDICATES) {
       emitFunctionTypeSignature(method, methodType);
       alwaysUseSignature = true;
     }
     functionTypeChecks.forEach((FunctionType functionType, bool knownSubtype) {
       if (knownSubtype) {
-        if (alwaysUseSignature) {
+        if (backend.rti.isSimpleFunctionType(functionType)) {
+          // Simple function types are always checked using predicates.
+          emitIsFunctionTypeTest(functionType);
+        } else if (alwaysUseSignature) {
           registerDynamicFunctionTypeCheck(functionType);
         } else {
           emitIsFunctionTypeTest(functionType);
         }
       }
     });
   }
 
   /**
    * Return a function that returns true if its argument is a class
@@ skipping 1950 matching lines @@
 
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;