Ignore portals in DOMRenderer.findHostInstance

**what is the change?:**
We want to ignore portals when firing a certain warning.

This allows us to get the host instance and ignore portals.

Also added a new snapshot recording while fixing things.

**why make this change?:**
Originally we had added a flag to the DOM node which was used for

rendering the portal, and then could notice and ignore children rendered
into those nodes.

However, it's better to just ignore portals in
`DOMRenderer.findHostInstance` because
 - we will not ignore a non-portal second child with this approach
 - we meant to ignore portals in this method anyway (according to a
   'TODO' comment)
 - this change only affects the DOM renderer, instead of changing code
   which is shared with RN and other renderers
 - we avoid adding unneeded expandos

**test plan:**
`yarn test`

**issue:**
facebook#8854

src/renderers/dom/fiber/ReactDOMFiberEntry.js

@@ -74,10 +74,10 @@ findDOMNode._injectFiber(function(fiber: Fiber) {
 
 type DOMContainer =
   | (Element & {
-    _reactRootContainer: ?Object,
+    _reactRootContainer: ?Object
   })
   | (Document & {
-    _reactRootContainer: ?Object,
+    _reactRootContainer: ?Object
   });
 
 type Container = Element | Document;
@@ -539,12 +539,7 @@ function renderSubtreeIntoContainer(
       const hostInstance = DOMRenderer.findHostInstance(
         container._reactRootContainer.current,
       );
-      const hostInstanceParentNode: any =
-        hostInstance && hostInstance.parentNode;
-      const hostInstanceParentIsPortal =
-        hostInstanceParentNode &&
-        hostInstanceParentNode.__reactInternalIsPortalContainer;
-      if (hostInstance && !hostInstanceParentIsPortal) {
+      if (hostInstance) {
         warning(
           hostInstance.parentNode === container,
           'render(...): It looks like the React-rendered content of this ' +

src/renderers/dom/fiber/__tests__/__snapshots__/ReactDOMFiber-test.js.snap

@@ -0,0 +1,3 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`ReactDOMFiber should warn when replacing a container which was manually updated outside of React 1`] = `""`;

src/renderers/shared/fiber/ReactFiberTreeReflection.js

@@ -25,10 +25,11 @@ if (__DEV__) {
 }
 
 var {
-  HostRoot,
+  ClassComponent,
   HostComponent,
+  HostRoot,
+  HostPortal,
   HostText,
-  ClassComponent,
 } = require('ReactTypeOfWork');
 
 var {NoEffect, Placement} = require('ReactTypeOfSideEffect');
@@ -241,8 +242,7 @@ exports.findCurrentHostFiber = function(parent: Fiber): Fiber | null {
   while (true) {
     if (node.tag === HostComponent || node.tag === HostText) {
       return node;
-    } else if (node.child) {
-      // TODO: If we hit a Portal, we're supposed to skip it.
+    } else if (node.child && node.tag !== HostPortal) {
       node.child.return = node;
       node = node.child;
       continue;