[react-packager] Fix the confused node_modules detection function

Summary:
@public

We have a function that detects whether a give file is to be treated as a node_modules. If so it doesn't have access to the haste module map. There is an exception to this rule which is a few modules that are allowed to do that. Currently thats react-native, react-tools, and parse.

The current implementation had a bug where if you had `react-native` (or react-tools etc) in the name before the actual package root then the detection will be off. This fixes the problem by starting from the `lastIndexOf('node_modules')` directory, that way nothing confuses us.

Test Plan:
./runJestTests.sh
export OSS, patch, run e2e test

react-packager/src/DependencyResolver/DependencyGraph/__tests__/DependencyGraph-test.js

@@ -2171,6 +2171,65 @@ describe('DependencyGraph', function() {
       });
     });
 
+    pit('should not be confused by prev occuring whitelisted names', function() {
+      var root = '/react-tools';
+      fs.__setMockFilesystem({
+        'react-tools': {
+          'index.js': [
+            '/**',
+            ' * @providesModule index',
+            ' */',
+            'require("shouldWork");',
+          ].join('\n'),
+          'node_modules': {
+            'react-tools': {
+              'package.json': JSON.stringify({
+                name: 'react-tools',
+                main: 'main.js',
+              }),
+              'main.js': [
+                '/**',
+                ' * @providesModule shouldWork',
+                ' */',
+              ].join('\n'),
+            },
+          },
+        }
+      });
+
+      var dgraph = new DependencyGraph({
+        roots: [root],
+        fileWatcher: fileWatcher,
+        assetExts: ['png', 'jpg'],
+      });
+      return dgraph.getOrderedDependencies('/react-tools/index.js').then(function(deps) {
+        expect(deps)
+          .toEqual([
+            {
+              id: 'index',
+              path: '/react-tools/index.js',
+              dependencies: ['shouldWork'],
+              isAsset: false,
+              isAsset_DEPRECATED: false,
+              isJSON: false,
+              isPolyfill: false,
+              resolution: undefined,
+            },
+            {
+              id: 'shouldWork',
+              path: '/react-tools/node_modules/react-tools/main.js',
+              dependencies: [],
+              isAsset: false,
+              isAsset_DEPRECATED: false,
+              isJSON: false,
+              isPolyfill: false,
+              resolution: undefined,
+            },
+          ]);
+      });
+    });
+
+
     pit('should ignore modules it cant find (assumes own require system)', function() {
       // For example SourceMap.js implements it's own require system.
       var root = '/root';

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

@@ -414,18 +414,20 @@ class DependencyGraph {
   }
 
   _isNodeModulesDir(file) {
-    const inNodeModules = file.indexOf('/node_modules/') !== -1;
+    let parts = path.normalize(file).split(path.sep);
+    const indexOfNodeModules = parts.lastIndexOf('node_modules');
 
-    if (!inNodeModules) {
+    if (indexOfNodeModules === -1) {
       return false;
     }
 
+    parts = parts.slice(indexOfNodeModules + 1);
+
     const dirs = this._opts.providesModuleNodeModules;
 
     for (let i = 0; i < dirs.length; i++) {
-      const index = file.indexOf(dirs[i]);
-      if (index !== -1) {
-        return file.slice(index).indexOf('/node_modules/') !== -1;
+      if (parts.indexOf(dirs[i]) > -1) {
+        return false;
       }
     }