Fixed flaky PlatformAppUrlRedirectorBrowserTest.WebviewNavigationNotIntercepted.

BUG=295721

Review URL: https://chromiumcodereview.appspot.com/24267019

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225118 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225118