Support runtime check of 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 ada5b1b0c76e21f08e063e362536f3efa975b075..017f3bec3f313dbd7b9a5685be64fde9a8cb8328 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
@@ -709,6 +709,25 @@ class Namer implements ClosureNamer {
 
   String operatorAsPrefix() => r'$as';
 
+  String operatorSignature() => r'$signature';
+
+  Map<FunctionType,String> functionTypeNameMap = new Map<FunctionType,String>();
+  FunctionTypeNamer functionTypeNamer = new FunctionTypeNamer();
+
+  String getFunctionTypeName(FunctionType functionType) {
+    return functionTypeNameMap.putIfAbsent(functionType, () {
+      String proposedName = functionTypeNamer.computeName(functionType);
+      String freshName = getFreshName(proposedName, usedInstanceNames,
+                                      suggestedInstanceNames, ensureSafe: true);
+      return freshName;
+    });
+  }
+
+  String operatorIsFunctionType(FunctionType type) {
+    // TODO(erikcorry): Reduce from $isx to ix when we are minifying.
+    return '${operatorIsPrefix()}${getFunctionTypeName(type)}';
+  }
+
   String operatorIs(Element element) {
     // TODO(erikcorry): Reduce from $isx to ix when we are minifying.
     return '${operatorIsPrefix()}${getName(element)}';
@@ -730,6 +749,16 @@ class Namer implements ClosureNamer {
     return '${operatorAsPrefix()}${getName(element)}';
   }
 
+  String signatureName(FunctionType type) {
+    ClassElement classElement = Types.getClassContext(type);
+    String signature = '${operatorSignature()}_${getFunctionTypeName(type)}';
+    if (classElement != null) {
+      return '${isolateAccess(classElement)}.$signature';
+    } else {
+      return '${CURRENT_ISOLATE}.$signature';
+    }
+  }
+
   String safeName(String name) => _safeName(name, jsReserved);
   String safeVariableName(String name) => _safeName(name, jsVariableReserved);
 
@@ -783,3 +812,47 @@ class Namer implements ClosureNamer {
     }
   }
 }
+
+class FunctionTypeNamer extends DartTypeVisitor {
+  StringBuffer sb;
+
+  String computeName(DartType type) {
+    sb = new StringBuffer();
+    visit(type);
+    return sb.toString();
+  }
+
+  visit(DartType type) {
+    type.accept(this, null);
+  }
+
+  visitType(DartType type, _) {
+    sb.write(type.name.slowToString());
+  }
+
+  visitFunctionType(FunctionType type, _) {
+    visit(type.returnType);
+    sb.write('_');
+    for (Link<DartType> link = type.parameterTypes;
+         !link.isEmpty;
+         link = link.tail) {
+      sb.write('_');
+      visit(link.head);
+    }
+    for (Link<DartType> link = type.optionalParameterTypes;
+         !link.isEmpty;
+         link = link.tail) {
+      sb.write('_');
+      visit(link.head);
+    }
+    if (!type.namedParameterTypes.isEmpty) {
+      for (Link<DartType> link = type.namedParameterTypes;
+          !link.isEmpty;
+          link = link.tail) {
+        sb.write('_');
+        visit(link.head);
+      }
+    }
+  }
+
+}