[Android,Ios]supporting button text resize

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,6 +1,22 @@
 <!--
 Thank you for sending the PR! We appreciate you spending the time to work on these changes. 
 
+- [x] Explain the **motivation** for making this change.
+- [x] Provide a **test plan** demonstrating that the code is solid.
+- [x] Match the **code formatting** of the rest of the codebase.
+- [x] Target the `master` branch, NOT a "stable" branch.
+
+## Motivation (required)
+I want to use 'react-native' more comfortable.
+
+What existing problem does the pull request solve?
+---------------------------------------------------------------------
+->in this version, 'button' component couldn't change text size in 'ios'. so, I added button's props 
+"textSize",be able to change button's text size.
+-------------------------------------------------------------
+
+ .  
+=======
 Help us understand your motivation by explaining why you decided to make this change.
 
 You can learn more about contributing to React Native here: http://facebook.github.io/react-native/docs/contributing.html
@@ -11,6 +27,13 @@ Happy contributing!
 
 (Write your motivation here.)
 
+If you have added code that should be tested, add tests.
+-----------------------------------------------------------------
+Ans:
+# **->testing video is here. text size is 10,20 and 30.
+[IMG_1944.MOV.zip](https://github.com/facebook/react-native/files/981039/IMG_1944.MOV.zip)**
+--------------------------------------------------------------------
+=======
 ## Test Plan
 
 (Write your test plan here. If you changed any code, please provide us with clear instructions on how you verified your changes work. Bonus points for screenshots and videos!)

Libraries/Components/Button.js

@@ -58,6 +58,7 @@ class Button extends React.Component<{
   accessibilityLabel?: ?string,
   disabled?: ?boolean,
   testID?: ?string,
+  textSize?: ?string,
 }> {
   static propTypes = {
     /**
@@ -84,6 +85,10 @@ class Button extends React.Component<{
      * Used to locate this view in end-to-end tests.
      */
     testID: PropTypes.string,
+    /**
+     * Used to change button's textSize
+     */
+    textSize: PropTypes.string,
   };
 
   render() {
@@ -94,6 +99,7 @@ class Button extends React.Component<{
       title,
       disabled,
       testID,
+      textSize,
     } = this.props;
     const buttonStyles = [styles.button];
     const textStyles = [styles.text];
@@ -104,6 +110,9 @@ class Button extends React.Component<{
         buttonStyles.push({backgroundColor: color});
       }
     }
+    if (textSize) {
+        textStyles.push({fontSize: parseInt(textSize)});
+    }
     const accessibilityTraits = ['button'];
     if (disabled) {
       buttonStyles.push(styles.buttonDisabled);
@@ -155,6 +164,7 @@ const styles = StyleSheet.create({
       textAlign: 'center',
       padding: 8,
       fontWeight: '500',
+      fontSize: 18,
     },
   }),
   buttonDisabled: Platform.select({