Add onContentSizeChange prop to WebView

Summary: Added support for WebViews to take in an onContentSizeChange prop, which will return a native event that contains the width and height of the html content in the WebView. Also moved the ContentSizeChangeEvent from the recyclerview dir to the uimanager/events dir

Reviewed By: andreicoman11

Differential Revision: D3775399

fbshipit-source-id: 19a0579f8345e5853cc7311b80f1f1393c77ab58

Libraries/Components/WebView/WebView.android.js

@@ -58,6 +58,7 @@ class WebView extends React.Component {
     automaticallyAdjustContentInsets: PropTypes.bool,
     contentInset: EdgeInsetsPropType,
     onNavigationStateChange: PropTypes.func,
+    onContentSizeChange: PropTypes.func,
     startInLoadingState: PropTypes.bool, // force WebView to show loadingView on first load
     style: View.propTypes.style,
 
@@ -219,6 +220,7 @@ class WebView extends React.Component {
         domStorageEnabled={this.props.domStorageEnabled}
         contentInset={this.props.contentInset}
         automaticallyAdjustContentInsets={this.props.automaticallyAdjustContentInsets}
+        onContentSizeChange={this.props.onContentSizeChange}
         onLoadingStart={this.onLoadingStart}
         onLoadingFinish={this.onLoadingFinish}
         onLoadingError={this.onLoadingError}