Reland "[iOS] Re-enable test 'testNetworkConnection' in device_check_egtest.mm"

This is a reland of 30ff548c
Original change's description:
> [iOS] Re-enable test 'testNetworkConnection' in device_check_egtest.mm
> 
> Since we are beginning to run external URL test again, and labs now has
> wifi. We need to re-enable the wifi checker test for swarming_cron use.
> 
> Bug: 763582
> Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
> Change-Id: I261b46c63c63160bfae49590fae9248f5d8ffdab
> Reviewed-on: https://chromium-review.googlesource.com/794341
> Reviewed-by: Sergey Berezin <sergeyberezin@chromium.org>
> Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
> Commit-Queue: Shenghua Zhang <shenghuazhang@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#519867}

Bug: 763582
Change-Id: I2bdf2a0903cf2f6c7307341f8570f80abf394ea5
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Reviewed-on: https://chromium-review.googlesource.com/809406Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Commit-Queue: Shenghua Zhang <shenghuazhang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521789}

ios/chrome/test/earl_grey/device_check_egtest.mm

@@ -20,9 +20,6 @@
 
 // Verifies Internet connectivity by navigating to browsingtest.appspot.com.
 - (void)testNetworkConnection {
-  // TODO(crbug.com/763582) Remove EARL_GREY_TEST_DISABLED if
-  // wifi tests running.
-  EARL_GREY_TEST_DISABLED(@"Test disabled due to Wifi issue.");
   [ChromeEarlGrey loadURL:GURL("http://browsingtest.appspot.com")];
   [ChromeEarlGrey waitForWebViewContainingText:"Window1"];
 }