Glenn suggests waiting for 2 seconds prior to retrying the download

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ace8dc83ee038e907dcb14ce09cd7e6584f315e3

commit ace8dc83ee038e907dcb14ce09cd7e6584f315e3
Author: pkotwicz <pkotwicz@chromium.org>
Date: Mon Oct 03 23:00:06 2016

Retry WebAPK download if fails for the first time.

The WebAPK server may send us the URL of the WebAPK to download prior to the
WebAPK being available at that URL. WebApkInstaller will sleep 2 seconds and
retry the download if the download fails.

BUG= 649704 
TBR=dfalcantara

Review-Url: https://codereview.chromium.org/2381023003
Cr-Commit-Position: refs/heads/master@{#422583}

[modify] https://crrev.com/ace8dc83ee038e907dcb14ce09cd7e6584f315e3/chrome/browser/android/webapk/webapk_installer.cc
[modify] https://crrev.com/ace8dc83ee038e907dcb14ce09cd7e6584f315e3/chrome/browser/android/webapk/webapk_installer.h