addes native unit test

Author: apremalal

packages/webview_flutter/webview_flutter_android/android/src/test/java/io/flutter/plugins/webviewflutter/WebSettingsTest.java

@@ -107,4 +107,10 @@ public void setBuiltInZoomControls() {
     testHostApiImpl.setBuiltInZoomControls(0L, true);
     verify(mockWebSettings).setBuiltInZoomControls(true);
   }
+
+  @Test
+  public void setTextZoom() {
+    testHostApiImpl.setTextZoom(0L, 100);
+    verify(mockWebSettings).setTextZoom(100);
+  }
 }