Fix flaky //scouting:scouting_test

The test occasionally fails because of the alerts that pop up when
navigating away from the page. I've failed to make protractor deal
with the alerts in a reliable way. So this patch turns them off.
There's a special hidden checkbox that the test checks. When it's
checked, the scouting application does not display alerts. It's hacky,
but it seems to work. Rather than failing ~10 out of 1000 times, the
test now fails 0 out of 1000 times.

Signed-off-by: Philipp Schrader <philipp.schrader@gmail.com>
Change-Id: I2e920771c1605464994d7877da2bbb62a2e69d1f
diff --git a/scouting/www/app.ng.html b/scouting/www/app.ng.html
index 2fafceb..d4ee5f4 100644
--- a/scouting/www/app.ng.html
+++ b/scouting/www/app.ng.html
@@ -1,3 +1,8 @@
+<!-- Hidden element for protractor to disable alerts. -->
+<form class="visually-hidden">
+  <input type="checkbox" name="block_alerts" value="1" id="block_alerts" #block_alerts>
+</form>
+
 <ul class="nav nav-tabs">
   <li class="nav-item">
     <a class="nav-link" [class.active]="tabIs('Entry')" (click)="switchTabTo('Entry')">Data Entry</a>