Ensure that all internal instances have consistent properties

Use preventExtensions so that we can't add expando properties to internal
instances. This ensures that the hidden class is kept more consistent.

src/browser/ui/ReactDOMComponent.js

@@ -147,6 +147,8 @@ function validateDangerousTag(tag) {
 function ReactDOMComponent(tag) {
   validateDangerousTag(tag);
   this._tag = tag;
+  this._renderedChildren = null;
+  this._previousStyleCopy = null;
 }
 
 ReactDOMComponent.displayName = 'ReactDOMComponent';

src/browser/ui/ReactDOMTextComponent.js

@@ -50,6 +50,10 @@ assign(ReactDOMTextComponent.prototype, {
     // TODO: This is really a ReactText (ReactNode), not a ReactElement
     this._currentElement = text;
     this._stringText = '' + text;
+
+    // Properties
+    this._rootNodeID = null;
+    this._mountIndex = 0;
   },
 
   /**

src/core/ReactComponent.js

@@ -118,6 +118,10 @@ var ReactComponent = {
       // We keep the old element and a reference to the pending element
       // to track updates.
       this._currentElement = element;
+
+      this._rootNodeID = null;
+      this._mountIndex = 0;
+      this._mountDepth = 0;
     },
 
     /**

src/core/ReactCompositeComponent.js

@@ -117,8 +117,11 @@ var ReactCompositeComponentMixin = assign({},
 
     this._pendingElement = null;
     this._pendingState = null;
+    this._pendingForceUpdate = false;
     this._compositeLifeCycleState = null;
 
+    this._renderedComponent = null;
+
     // Children can be either an array or more than one argument
     ReactComponent.Mixin.construct.apply(this, arguments);
 

src/core/instantiateReactComponent.js

@@ -118,6 +118,14 @@ function instantiateReactComponent(node, parentCompositeType) {
   // Sets up the instance. This can probably just move into the constructor now.
   instance.construct(node);
 
+  // Internal instances should fully constructed at this point, so they should
+  // not get any new fields added to them at this point.
+  if (__DEV__) {
+    if (Object.preventExtensions) {
+      Object.preventExtensions(instance);
+    }
+  }
+
   return instance;
 }