The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9493672631e4b3073a5c246c57921b01535be093

commit 9493672631e4b3073a5c246c57921b01535be093
Author: Sylvain Defresne <sdefresne@chromium.org>
Date: Fri Mar 02 22:33:16 2018

Remove TabDelegate protocol

Change PreloadController to register itself as WebStateObserver
for Tab's WebState and CRWWebDelegate for Tab's CRWWebController.
Move code cancelling the pre-rendering to PreloadController.

There is one change that is quite subtle: the PreloadController
need to forward CRWWebDelegate methods to Tab if Tab implement
them as there can only be one CRWWebDelegate registered. It also
needs to register Tab as CRWWebDelegate at the end of pre-render.

Bug:  661663 
Change-Id: I64655ed8deef1cbad1a02a40b4d4b5d6b853d2eb
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/941329
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540663}
[modify] https://crrev.com/9493672631e4b3073a5c246c57921b01535be093/ios/chrome/browser/prerender/preload_controller.h
[modify] https://crrev.com/9493672631e4b3073a5c246c57921b01535be093/ios/chrome/browser/prerender/preload_controller.mm
[modify] https://crrev.com/9493672631e4b3073a5c246c57921b01535be093/ios/chrome/browser/tabs/BUILD.gn
[modify] https://crrev.com/9493672631e4b3073a5c246c57921b01535be093/ios/chrome/browser/tabs/tab.h
[modify] https://crrev.com/9493672631e4b3073a5c246c57921b01535be093/ios/chrome/browser/tabs/tab.mm
[delete] https://crrev.com/33be507c236e6667c88e480195e5448a61ffb436/ios/chrome/browser/tabs/tab_delegate.h