Reland "Disable WebStateTest.MessageFromIFrame test."

This is a reland of 0c2015e1

TBR=eugenebut@chromium.org

Original change's description:
> Disable WebStateTest.MessageFromIFrame test.
>
> TBR=eugenebut@chromium.org
>
> Bug: 857129
> Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
> Change-Id: I407a6464e71296cc15eef43bf7ed2a8ca8181909
> Reviewed-on: https://chromium-review.googlesource.com/1117300
> Commit-Queue: Mike Dougherty <michaeldo@chromium.org>
> Reviewed-by: Mike Dougherty <michaeldo@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#570882}

Bug: 857129
Change-Id: I62a341ccebb1ceef892a2f07eb0faae4d87476d7
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Reviewed-on: https://chromium-review.googlesource.com/1118685Reviewed-by: Mike Dougherty <michaeldo@chromium.org>
Commit-Queue: Mike Dougherty <michaeldo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571159}

ios/web/web_state/web_state_unittest.mm

@@ -211,7 +211,8 @@ TEST_F(WebStateTest, MessageFromMainFrame) {
 
 // Tests that message sent from main frame triggers the ScriptCommandCallback
 // with |is_main_frame| = false.
-TEST_F(WebStateTest, MessageFromIFrame) {
+// TODO(crbug.com/857129): Re-enable this test.
+TEST_F(WebStateTest, DISABLED_MessageFromIFrame) {
   // Add a script command handler.
   __block bool message_received = false;
   __block bool message_from_main_frame = false;