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Added the following test cases:
 - testReloadPageAfterServerIsDown
 - testGoForwardAfterServerIsDownAndReload
 - testGoBackFromErrorPage

Bug: 725241
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I6a872e6691c66ff6facd100cdb90607488738ff6
Reviewed-on: https://chromium-review.googlesource.com/1043074Reviewed-by: Danyao Wang <danyao@chromium.org>
Commit-Queue: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556082}