breaking test and fix for browser field mapping from package to file

Summary:
breaks on mappings like:

```json
"browser": {
  "node-package": "./dir/browser.js"
}
```
Closes https://github.com/facebook/react-native/pull/5505

Reviewed By: svcscm

Differential Revision: D2860579

Pulled By: androidtrunkagent

fb-gh-sync-id: 0d64c0999c47a6cbbf084cc8e0c8a6ea209b0880

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

@@ -264,20 +264,33 @@ class ResolutionRequest {
     });
   }
 
+  _resolveFileOrDir(fromModule, toModuleName) {
+    const potentialModulePath = isAbsolutePath(toModuleName) ?
+        toModuleName :
+        path.join(path.dirname(fromModule.path), toModuleName);
+
+    return this._redirectRequire(fromModule, potentialModulePath).then(
+      realModuleName => this._tryResolve(
+        () => this._loadAsFile(realModuleName, fromModule, toModuleName),
+        () => this._loadAsDir(realModuleName, fromModule, toModuleName)
+      )
+    );
+  }
+
   _resolveNodeDependency(fromModule, toModuleName) {
     if (toModuleName[0] === '.' || toModuleName[1] === '/') {
-      const potentialModulePath = isAbsolutePath(toModuleName) ?
-              toModuleName :
-              path.join(path.dirname(fromModule.path), toModuleName);
-      return this._redirectRequire(fromModule, potentialModulePath).then(
-        realModuleName => this._tryResolve(
-          () => this._loadAsFile(realModuleName, fromModule, toModuleName),
-          () => this._loadAsDir(realModuleName, fromModule, toModuleName)
-        )
-      );
+      return this._resolveFileOrDir(fromModule, toModuleName)
     } else {
       return this._redirectRequire(fromModule, toModuleName).then(
         realModuleName => {
+          if (realModuleName[0] === '.' || realModuleName[1] === '/') {
+            // derive absolute path /.../node_modules/fromModuleDir/realModuleName
+            let fromModuleParentIdx = fromModule.path.lastIndexOf('node_modules/') + 13
+            let fromModuleDir = fromModule.path.slice(0, fromModule.path.indexOf('/', fromModuleParentIdx))
+            let absPath = path.join(fromModuleDir, realModuleName)
+            return this._resolveFileOrDir(fromModule, absPath)
+          }
+
           const searchQueue = [];
           for (let currDir = path.dirname(fromModule.path);
                currDir !== path.parse(fromModule.path).root;

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

@@ -1774,6 +1774,85 @@ describe('DependencyGraph', function() {
         });
       });
 
+      pit('should support browser mapping of a package to a file ("' + fieldName + '")', function() {
+        var root = '/root';
+        fs.__setMockFilesystem({
+          'root': {
+            'index.js': [
+              '/**',
+              ' * @providesModule index',
+              ' */',
+              'require("aPackage")',
+            ].join('\n'),
+            'aPackage': {
+              'package.json': JSON.stringify(replaceBrowserField({
+                name: 'aPackage',
+                browser: {
+                  'node-package': './dir/browser.js',
+                },
+              }, fieldName)),
+              'index.js': 'require("./dir/ooga")',
+              'dir': {
+                'ooga.js': 'require("node-package")',
+                'browser.js': 'some browser code',
+              },
+              'node-package': {
+                'package.json': JSON.stringify({
+                  'name': 'node-package',
+                }),
+                'index.js': 'some node code',
+              },
+            },
+          },
+        });
+
+        const dgraph = new DependencyGraph({
+          ...defaults,
+          roots: [root],
+        });
+        return getOrderedDependenciesAsJSON(dgraph, '/root/index.js').then(function(deps) {
+          expect(deps)
+            .toEqual([
+              { id: 'index',
+                path: '/root/index.js',
+                dependencies: ['aPackage'],
+                isAsset: false,
+                isAsset_DEPRECATED: false,
+                isJSON: false,
+                isPolyfill: false,
+                resolution: undefined,
+              },
+              { id: 'aPackage/index.js',
+                path: '/root/aPackage/index.js',
+                dependencies: ['./dir/ooga'],
+                isAsset: false,
+                isAsset_DEPRECATED: false,
+                isJSON: false,
+                isPolyfill: false,
+                resolution: undefined,
+              },
+              { id: 'aPackage/dir/ooga.js',
+                path: '/root/aPackage/dir/ooga.js',
+                dependencies: ['node-package'],
+                isAsset: false,
+                isAsset_DEPRECATED: false,
+                isJSON: false,
+                isPolyfill: false,
+                resolution: undefined,
+              },
+              { id: 'aPackage/dir/browser.js',
+                path: '/root/aPackage/dir/browser.js',
+                dependencies: [],
+                isAsset: false,
+                isAsset_DEPRECATED: false,
+                isJSON: false,
+                isPolyfill: false,
+                resolution: undefined,
+              },
+            ]);
+        });
+      });
+
       pit('should support browser mapping for packages ("' + fieldName + '")', function() {
         var root = '/root';
         fs.__setMockFilesystem({