Move defaultProps resolution to the descriptor factory

Moves the defaultProps resolution to the descriptor factory.

src/core/ReactCompositeComponent.js

@@ -939,25 +939,13 @@ var ReactCompositeComponentMixin = {
    * @private
    */
   _processProps: function(newProps) {
-    var defaultProps = this.constructor.defaultProps;
-    var props;
-    if (defaultProps) {
-      props = merge(newProps);
-      for (var propName in defaultProps) {
-        if (typeof props[propName] === 'undefined') {
-          props[propName] = defaultProps[propName];
-        }
-      }
-    } else {
-      props = newProps;
-    }
     if (__DEV__) {
       var propTypes = this.constructor.propTypes;
       if (propTypes) {
-        this._checkPropTypes(propTypes, props, ReactPropTypeLocations.prop);
+        this._checkPropTypes(propTypes, newProps, ReactPropTypeLocations.prop);
       }
     }
-    return props;
+    return newProps;
   },
 
   /**

src/core/ReactDescriptor.js

@@ -158,6 +158,8 @@ ReactDescriptor.createDescriptor = function(type, config, children) {
     }
   }
 
+  var propName;
+
   // Reserved names are extracted
   var props = {};
 
@@ -168,16 +170,14 @@ ReactDescriptor.createDescriptor = function(type, config, children) {
     ref = config.ref === undefined ? null : config.ref;
     key = config.key === undefined ? null : '' + config.key;
     // Remaining properties are added to a new props object
-    for (var propName in config) {
+    for (propName in config) {
       if (config.hasOwnProperty(propName) &&
           !RESERVED_PROPS.hasOwnProperty(propName)) {
         props[propName] = config[propName];
       }
     }
   }
 
-  // TODO: fill in defaultProps here, after transferPropsTo is gone
-
   // Children can be more than one argument, and those are transferred onto
   // the newly allocated props object.
   var childrenLength = arguments.length - 2;
@@ -191,6 +191,16 @@ ReactDescriptor.createDescriptor = function(type, config, children) {
     props.children = childArray;
   }
 
+  // Resolve default props
+  if (type.defaultProps) {
+    var defaultProps = type.defaultProps;
+    for (propName in defaultProps) {
+      if (typeof props[propName] === 'undefined') {
+        props[propName] = defaultProps[propName];
+      }
+    }
+  }
+
   return new ReactDescriptor(
     type,
     key,

src/core/__tests__/ReactPropTransferer-test.js

@@ -164,7 +164,7 @@ describe('ReactPropTransferer', function() {
     );
   });
 
-  it('should not use the default when a prop is transfered', function() {
+  it('uses the default instead of the transferred prop (regress)', function() {
 
     var Child = React.createClass({
 
@@ -175,7 +175,7 @@ describe('ReactPropTransferer', function() {
       },
 
       render: function() {
-        expect(this.props.x).toBe(5);
+        expect(this.props.x).toBe(2);
         return <div />;
       }