Speculative fix for XR timeout

Halves the number of iterations in TestControllerInputRegistered. With
the old value of 10, the test runtime was ~9 seconds, which was
uncomfortably close to the default JS timeout of 10 seconds. It's
suspected that if the test machine was a bit slow, the test would end
up timing out. 5 iterations should still be plenty to verify that input
works.

TBR=alcooper@chromium.org

Bug: 984989
Change-Id: Ie6c67725c692ea47aa83a4adc3c8fcf0aa9e9692
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1706774Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Alexander Cooper <alcooper@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#678399}

chrome/browser/vr/webxr_vr_input_browser_test.cc

@@ -696,7 +696,7 @@ WEBXR_VR_ALL_RUNTIMES_BROWSER_TEST_F(TestControllerInputRegistered) {
       t->GetFileUrlForHtmlTestFile("test_webxr_input"));
   t->EnterSessionWithUserGestureOrFail();
 
-  unsigned int num_iterations = 10;
+  unsigned int num_iterations = 5;
   t->RunJavaScriptOrFail("stepSetupListeners(" +
                          base::NumberToString(num_iterations) + ")");