Use predicates to check simple function types.

sdk/lib/_internal/compiler/implementation/js_backend/namer.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart b/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
index 7a6e6f3abda157d9e18a268c85b16c578da6c22d..e1246bf341ad488b8eca9f14fb80903ee1d0ace9 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
@@ -225,7 +225,8 @@ class Namer implements ClosureNamer {
         popularNameCounters = new Map<String, int>(),
         constantNames = new Map<Constant, String>(),
         constantLongNames = new Map<Constant, String>(),
-        constantHasher = new ConstantCanonicalHasher(compiler);
+        constantHasher = new ConstantCanonicalHasher(compiler),
+        functionTypeNamer = new FunctionTypeNamer(compiler);
 
   String get isolateName => 'Isolate';
   String get isolatePropertiesName => r'$isolateProperties';
@@ -800,7 +801,7 @@ class Namer implements ClosureNamer {
 
   Map<FunctionType,String> functionTypeNameMap =
       new Map<FunctionType,String>();
-  FunctionTypeNamer functionTypeNamer = new FunctionTypeNamer();
+  final FunctionTypeNamer functionTypeNamer;
 
   String getFunctionTypeName(FunctionType functionType) {
     return functionTypeNameMap.putIfAbsent(functionType, () {
@@ -1223,8 +1224,13 @@ class ConstantCanonicalHasher implements ConstantVisitor<int> {
 }
 
 class FunctionTypeNamer extends DartTypeVisitor {
+  final Compiler compiler;
   StringBuffer sb;
 
+  FunctionTypeNamer(this.compiler);
+
+  JavaScriptBackend get backend => compiler.backend;
+
   String computeName(DartType type) {
     sb = new StringBuffer();
     visit(type);
@@ -1240,6 +1246,10 @@ class FunctionTypeNamer extends DartTypeVisitor {
   }
 
   visitFunctionType(FunctionType type, _) {
+    if (backend.rti.isSimpleFunctionType(type)) {
+      sb.write('args${type.parameterTypes.slowLength()}');
+      return;
+    }
     visit(type.returnType);
     sb.write('_');
     for (Link<DartType> link = type.parameterTypes;