Added inheritance for StyleSheet.

Libraries/StyleSheet/StyleSheet.js

@@ -13,6 +13,7 @@
 
 var StyleSheetRegistry = require('StyleSheetRegistry');
 var StyleSheetValidation = require('StyleSheetValidation');
+var StyleSheetInheritance = require('StyleSheetInheritance');
 
 /**
  * A StyleSheet is an abstraction similar to CSS StyleSheets
@@ -62,6 +63,7 @@ class StyleSheet {
   static create(obj: {[key: string]: any}): {[key: string]: number} {
     var result = {};
     for (var key in obj) {
+      obj[key] = StyleSheetInheritance.resolve( key, obj );
       StyleSheetValidation.validateStyle(key, obj);
       result[key] = StyleSheetRegistry.registerStyle(obj[key]);
     }

Libraries/StyleSheet/StyleSheetInheritance.js

@@ -0,0 +1,78 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @providesModule StyleSheetInheritance
+ * @flow
+ */
+
+var _ = require( 'underscore' );
+
+/**
+ * The StyleSheetInheritance object can be used to resolve StyleSheetInheritance.
+ *
+ * Instead of writing:
+ *```javascript
+ *  var styles = StyleSheet.create( {
+ *    viewStyle: {
+ *      marginTop: 5,
+ *      marginBottom: 5,
+ *      backgroundColor: '#bbbbbb',
+ *      flex: 1
+ *    },
+ *    viewStyleEdit: {
+ *      marginTop: 20,
+ *      marginBottom: 5,
+ *      backgroundColor: '#fffffff',
+ *      flex: 1
+ *    }
+ *  });
+ *```
+ *
+ *  You can simplify to:
+ *   ```javascript
+ *   var styles = StyleSheet.create( {
+ *    viewStyle: {
+ *      marginTop: 5,
+ *      marginBottom: 5,
+ *      backgroundColor: '#bbbbbb',
+ *      flex: 1
+ *    },
+ *    viewStyleEdit: ["viewStyle". {
+ *      marginTop: 20,
+ *      backgroundColor: '#fffffff'
+ *    } ]
+ *  }); *
+ *  ```
+ *
+ *  The StyleSheetInheritance takes care of resolving these dependencies.
+ *
+ */
+class StyleSheetInheritance {
+  static resolve( name, styles ) {
+    if (!_.isArray( styles[name])) {
+      return styles[name];
+    }
+
+    var resultStyle = {};
+
+    var parentObjects = [];
+    for (var index in styles[name]) {
+      var parentName = styles[name][index];
+      if (typeof parentName === 'string') {
+        if (styles.hasOwnProperty(parentName)) {
+          _.extend(resultStyle, styles[parentName]);
+        }
+      }
+    }
+    _.extend(resultStyle, _.last(styles[name]));
+
+    return resultStyle;
+  }
+}
+
+module.exports = StyleSheetInheritance;