Move _pendingX into ReactCompositeComponent

Since setProps can no longer be called on anything but composites, we can
move this complexity into ReactCompositeComponent.

src/browser/ui/ReactDOMComponent.js

@@ -291,11 +291,9 @@ ReactDOMComponent.Mixin = {
       return;
     }
 
-    ReactComponent.Mixin.receiveComponent.call(
-      this,
-      nextElement,
-      transaction
-    );
+    var prevElement = this._currentElement;
+    this._currentElement = nextElement;
+    this.updateComponent(transaction, prevElement, nextElement);
   },
 
   /**

src/core/ReactComponent.js

@@ -115,13 +115,9 @@ var ReactComponent = {
      * @internal
      */
     construct: function(element) {
-      // See ReactUpdates.
-      this._pendingCallbacks = null;
-
       // We keep the old element and a reference to the pending element
       // to track updates.
       this._currentElement = element;
-      this._pendingElement = null;
     },
 
     /**
@@ -167,41 +163,6 @@ var ReactComponent = {
       unmountIDFromEnvironment(this._rootNodeID);
       // Reset all fields
       this._rootNodeID = null;
-      this._pendingCallbacks = null;
-      this._pendingElement = null;
-    },
-
-    /**
-     * Given a new instance of this component, updates the rendered DOM nodes
-     * as if that instance was rendered instead.
-     *
-     * Subclasses that override this method should make sure to invoke
-     * `ReactComponent.Mixin.receiveComponent.call(this, ...)`.
-     *
-     * @param {object} nextComponent Next set of properties.
-     * @param {ReactReconcileTransaction} transaction
-     * @internal
-     */
-    receiveComponent: function(nextElement, transaction) {
-      this._pendingElement = nextElement;
-      this.performUpdateIfNecessary(transaction);
-    },
-
-    /**
-     * If `_pendingElement` is set, update the component.
-     *
-     * @param {ReactReconcileTransaction} transaction
-     * @internal
-     */
-    performUpdateIfNecessary: function(transaction) {
-      if (this._pendingElement == null) {
-        return;
-      }
-      var prevElement = this._currentElement;
-      var nextElement = this._pendingElement;
-      this._currentElement = nextElement;
-      this._pendingElement = null;
-      this.updateComponent(transaction, prevElement, nextElement);
     },
 
     /**

src/core/ReactCompositeComponent.js

@@ -115,11 +115,15 @@ var ReactCompositeComponentMixin = assign({},
     this._instance.context = null;
     this._instance.refs = emptyObject;
 
+    this._pendingElement = null;
     this._pendingState = null;
     this._compositeLifeCycleState = null;
 
     // Children can be either an array or more than one argument
     ReactComponent.Mixin.construct.apply(this, arguments);
+
+    // See ReactUpdates.
+    this._pendingCallbacks = null;
   },
 
   /**
@@ -234,6 +238,9 @@ var ReactCompositeComponentMixin = assign({},
     // Reset pending fields
     this._pendingState = null;
     this._pendingForceUpdate = false;
+    this._pendingCallbacks = null;
+    this._pendingElement = null;
+
     ReactComponent.Mixin.unmountComponent.call(this);
 
     // Delete the reference from the instance to this internal representation
@@ -505,11 +512,8 @@ var ReactCompositeComponentMixin = assign({},
       return;
     }
 
-    ReactComponent.Mixin.receiveComponent.call(
-      this,
-      nextElement,
-      transaction
-    );
+    this._pendingElement = nextElement;
+    this.performUpdateIfNecessary(transaction);
   },
 
   /**