Add simple React.createDescriptor hook

This is the minimal runtime change we need to switch the JSX syntax to resolve
to React.createDescriptor(...)

src/browser/ui/React.js

@@ -53,6 +53,10 @@ var React = {
     EventPluginUtils.useTouchEvents = shouldUseTouch;
   },
   createClass: ReactCompositeComponent.createClass,
+  createDescriptor: function(type, props, children) {
+    var args = Array.prototype.slice.call(arguments, 1);
+    return type.apply(null, args);
+  },
   constructAndRenderComponent: ReactMount.constructAndRenderComponent,
   constructAndRenderComponentByID: ReactMount.constructAndRenderComponentByID,
   renderComponent: ReactPerf.measure(

src/core/__tests__/ReactDescriptor-test.js

@@ -45,4 +45,17 @@ describe('ReactDescriptor', function() {
     expect(ReactDescriptor.isValidDescriptor(React.DOM.div)).toEqual(false);
     expect(ReactDescriptor.isValidDescriptor(Component)).toEqual(false);
   });
+
+  it('immediately calls the type passed to createDescriptor', function() {
+    var a = 1, b = 2, c = 3, d = 4;
+
+    var foo = jest.genMockFunction();
+    foo.mockReturnValue(d);
+
+    var result = React.createDescriptor(foo, a, b, c);
+
+    expect(result).toBe(d);
+    expect(foo).toBeCalledWith(a, b, c);
+  });
+
 });