Add hasIcon static method API (#666)

* Add hasIcon static method to Icon class

* FIx CI

* FIx code styles

* Avoiding creating new array

* Update readme

README.md

@@ -215,6 +215,8 @@ Any [Text property](http://facebook.github.io/react-native/docs/text.html) and t
 |**`name`**|What icon to show, see Icon Explorer app or one of the links above. |*None*|
 |**`color`**|Color of the icon. |*Inherited*|
 
+You can use `Icon.hasIcon(name)` to check if the name is valid in current icon set.
+
 ### Styling
 Since `Icon` builds on top of the `Text` component, most [style properties](http://facebook.github.io/react-native/docs/style.html) will work as expected, you might find it useful to play around with these:
 

lib/create-icon-set.js

@@ -159,6 +159,10 @@ export default function createIconSet(glyphMap, fontFamily, fontFile) {
     return Promise.resolve();
   }
 
+  function hasIcon(name) {
+    return Object.prototype.hasOwnProperty.call(glyphMap, name);
+  }
+
   Icon.Button = createIconButtonComponent(Icon);
   Icon.TabBarItem = createTabBarItemIOSComponent(
     IconNamePropType,
@@ -171,6 +175,7 @@ export default function createIconSet(glyphMap, fontFamily, fontFile) {
   );
   Icon.getImageSource = getImageSource;
   Icon.loadFont = loadFont;
+  Icon.hasIcon = hasIcon;
 
   return Icon;
 }