Accept number for size prop

Previously, size can only accept either 'small' or 'large'.
And to obtain a custom size, scale transformation is used.
This is to let users to possibly pass number value to define
ActivityIndicator's size.

Libraries/Components/ActivityIndicator/ActivityIndicator.js

@@ -41,11 +41,11 @@ const ActivityIndicator = React.createClass({
     color: ColorPropType,
     /**
      * Size of the indicator. Small has a height of 20, large has a height of 36.
-     * Other sizes can be obtained using a scale transform.
+     * Other sizes can be obtained by passing a number of by using a scale transform.
      */
-    size: PropTypes.oneOf([
-      'small',
-      'large',
+    size: PropTypes.oneOfType([
+      PropTypes.oneOf(['small','large',]),
+      PropTypes.number,
     ]),
     /**
      * Whether the indicator should hide when not animating (true by default).
@@ -67,14 +67,20 @@ const ActivityIndicator = React.createClass({
   render() {
     const {onLayout, style, ...props} = this.props;
     let sizeStyle;
-    switch (props.size) {
-      case 'small':
-        sizeStyle = styles.sizeSmall;
-        break;
-      case 'large':
-        sizeStyle = styles.sizeLarge;
-        break;
+    if (isNaN(props.size)) {
+      switch (props.size) {
+        case 'small':
+          sizeStyle = styles.sizeSmall;
+          break;
+        case 'large':
+          sizeStyle = styles.sizeLarge;
+          break;
+      }
+
+    } else {
+      sizeStyle = {height: props.size, width: props.size};
     }
+
     return (
       <View
         onLayout={onLayout}
@@ -84,7 +90,7 @@ const ActivityIndicator = React.createClass({
           style={sizeStyle}
           styleAttr="Normal"
           indeterminate
-        />
+         />
       </View>
     );
   }