Fixed bug where 'JS$Function' was being generated instead of just 'Function' for the TypeScript Function type

Author: derekxu16

lib/facade_converter.ts

@@ -411,6 +411,11 @@ export class FacadeConverter extends base.TranspilerBase {
       // https://www.typescriptlang.org/docs/handbook/utility-types.html
       const type = node.typeName.getText();
       switch (type) {
+        case 'Function':
+          // We check this case to prevent generating JS$Function for the name; the keyword
+          // Function may be used as a type but not in other cases
+          name = 'Function';
+          break;
         case 'Partial':
           // Partial<X> is currently the same as X since all types are nullable in Dart
           name = this.generateDartTypeName(node.typeArguments[0]);

test/type_test.ts

@@ -101,6 +101,11 @@ external set x(List<String> v);`);
 external String Function(String) get x;
 @JS()
 external set x(String Function(String) v);`);
+
+    expectTranslate('declare var a: Function').to.equal(`@JS()
+external Function get a;
+@JS()
+external set a(Function v);`);
   });
 
   describe('TypeScript utility types and other mapped types', () => {