unselectedItemTintColor property available since iOS10

Summary:
**motivation:**

make possible to use new tab bar property.

![1475603157804](https://cloud.githubusercontent.com/assets/1488195/19085757/8b7cc8a4-8a7c-11e6-82c7-7c76313fb545.jpg)

It is not working for previous versions but not failing.
https://developer.apple.com/reference/uikit/uitabbar/1648949-unselecteditemtintcolor
Closes https://github.com/facebook/react-native/pull/10241

Differential Revision: D4168046

Pulled By: mmmulani

fbshipit-source-id: aa0c9b36cbdbc50a9a60bbbc658355c3066ba1a5

Examples/UIExplorer/js/TabBarIOSExample.js

@@ -58,6 +58,7 @@ class TabBarExample extends React.Component {
       <TabBarIOS
         unselectedTintColor="yellow"
         tintColor="white"
+        unselectedItemTintColor="red"
         barTintColor="darkslateblue">
         <TabBarIOS.Item
           title="Blue Tab"

Libraries/Components/TabBarIOS/TabBarIOS.ios.js

@@ -24,6 +24,7 @@ class TabBarIOS extends React.Component {
     style?: $FlowFixMe,
     unselectedTintColor?: $FlowFixMe,
     tintColor?: $FlowFixMe,
+    unselectedItemTintColor?: $FlowFixMe,
     barTintColor?: $FlowFixMe,
     translucent?: boolean,
     itemPositioning?: 'fill' | 'center' | 'auto',
@@ -42,6 +43,10 @@ class TabBarIOS extends React.Component {
      * Color of the currently selected tab icon
      */
     tintColor: ColorPropType,
+    /**
+     * Color of unselected tab icons. Available since iOS 10.
+     */
+    unselectedItemTintColor: ColorPropType,
     /**
      * Background color of the tab bar
      */
@@ -67,6 +72,7 @@ class TabBarIOS extends React.Component {
       <RCTTabBar
         style={[styles.tabGroup, this.props.style]}
         unselectedTintColor={this.props.unselectedTintColor}
+        unselectedItemTintColor={this.props.unselectedItemTintColor}
         tintColor={this.props.tintColor}
         barTintColor={this.props.barTintColor}
         itemPositioning={this.props.itemPositioning}

React/Views/RCTTabBar.m

@@ -149,6 +149,14 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithCoder:(NSCoder *)aDecoder)
   _tabController.tabBar.translucent = translucent;
 }
 
+- (void)setUnselectedItemTintColor:(UIColor *)unselectedItemTintColor {
+#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_10_0
+  if ([_tabController.tabBar respondsToSelector:@selector(unselectedItemTintColor)]) {
+    _tabController.tabBar.unselectedItemTintColor = unselectedItemTintColor;
+  }
+#endif
+}
+
 - (UITabBarItemPositioning)itemPositoning
 {
 #if TARGET_OS_TV

React/Views/RCTTabBarManager.m

@@ -36,5 +36,6 @@ RCT_EXPORT_VIEW_PROPERTY(tintColor, UIColor)
 RCT_EXPORT_VIEW_PROPERTY(barTintColor, UIColor)
 RCT_EXPORT_VIEW_PROPERTY(translucent, BOOL)
 RCT_EXPORT_VIEW_PROPERTY(itemPositioning, UITabBarItemPositioning)
+RCT_EXPORT_VIEW_PROPERTY(unselectedItemTintColor, UIColor)
 
 @end