Fix WebView vulnerability by disallowing file access

Fix webvuew vulnerability inside captiveportal activity by disallowing
access private file in app's sandbox.

Bug: 150610071
Test: Build
Change-Id: I67e695478476b6ee9cf21ed41213f25441d9776a

packages/CarrierDefaultApp/src/com/android/carrierdefaultapp/CaptivePortalLoginActivity.java

@@ -106,6 +106,7 @@ public class CaptivePortalLoginActivity extends Activity {
         webSettings.setSupportZoom(true);
         webSettings.setBuiltInZoomControls(true);
         webSettings.setDomStorageEnabled(true);
+        webSettings.setAllowFileAccess(false);
         mWebViewClient = new MyWebViewClient();
         mWebView.setWebViewClient(mWebViewClient);
         mWebView.setWebChromeClient(new MyWebChromeClient());