Consume react, fbjs from npm

Summary:
We don't (yet) treat these the same as any other modules because we still have special resolution rules for them in the packager allowing the use of `providesModule`, but I believe this allows people to use npm react in their RN projects and not have duplicate copies of React. Fixes facebook/react-native#2985.

This relies on fbjs 0.6, which includes `.flow` files alongside the `.js` files to allow them to be typechecked without additional configuration. This also uses react 0.14.5, which shims a couple of files (as `.native.js`) to avoid DOM-specific bits. Once we fix these in React, we will use the same code on web and native. Hopefully we can also remove the packager support I'm adding here for `.native.js`.

This diff is not the desired end state for us – ideally the packager would know nothing of react or fbjs, and we'll get there eventually by not relying on `providesModule` in order to load react and fbjs modules. (fbjs change posted here but not merged yet: https://github.com/facebook/fbjs/pull/84.)

This should also allow relay to work seamlessly with RN, but I haven't verified this.

public

Reviewed By: sebmarkbage

Differential Revision: D2786197

fb-gh-sync-id: ff50f28445e949edc9501f4b599df7970813870d

packager/react-packager/src/DependencyResolver/DependencyGraph/ResolutionRequest.js

@@ -18,6 +18,7 @@ const Promise = require('promise');
 class ResolutionRequest {
   constructor({
     platform,
+    preferNativePlatform,
     entryPath,
     hasteMap,
     deprecatedAssetMap,
@@ -26,6 +27,7 @@ class ResolutionRequest {
     fastfs,
   }) {
     this._platform = platform;
+    this._preferNativePlatform = preferNativePlatform;
     this._entryPath = entryPath;
     this._hasteMap = hasteMap;
     this._deprecatedAssetMap = deprecatedAssetMap;
@@ -329,6 +331,9 @@ class ResolutionRequest {
       } else if (this._platform != null &&
                  this._fastfs.fileExists(potentialModulePath + '.' + this._platform + '.js')) {
         file = potentialModulePath + '.' + this._platform + '.js';
+      } else if (this._preferNativePlatform &&
+                 this._fastfs.fileExists(potentialModulePath + '.native.js')) {
+        file = potentialModulePath + '.native.js';
       } else if (this._fastfs.fileExists(potentialModulePath + '.js')) {
         file = potentialModulePath + '.js';
       } else if (this._fastfs.fileExists(potentialModulePath + '.json')) {