Android: Allow WebView to handle about:blank

Summary:
On some devices, we saw many Chrome windows open when the WebView attempted to send the user to about:blank. This change allows the WebView to handle about:blank which prevents the Chrome windows from opening and gives the user a better experience.

Verified that the WebView no longer opens the device's browser when navigating to about:blank. My team has been using this change in our app.

Adam Comella
Microsoft Corp.
Closes https://github.com/facebook/react-native/pull/14173

Differential Revision: D5142352

Pulled By: hramos

fbshipit-source-id: 1070d4381b385a5bf1829fd8e97efba2045f7968

ReactAndroid/src/main/java/com/facebook/react/views/webview/ReactWebViewManager.java

@@ -137,7 +137,7 @@ public class ReactWebViewManager extends SimpleViewManager<WebView> {
     @Override
     public boolean shouldOverrideUrlLoading(WebView view, String url) {
         if (url.startsWith("http://") || url.startsWith("https://") ||
-            url.startsWith("file://")) {
+            url.startsWith("file://") || url.equals("about:blank")) {
           return false;
         } else {
           try {