Bookmarks is dismissed multiple times in two ways:
1) When opening a url, BVC's loadUrl dismisses bookmarks explicitly, and then bookmarks dismisses itself.
2) BVC's clearPresentedState dismisses bookmarks, then continues to dismiss self.presentedViewController.  When bookmarks is visible, this ends up dismissing it twice.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a668c02effc76b2dd141a79dd2487a19477396b3

commit a668c02effc76b2dd141a79dd2487a19477396b3
Author: Rohit Rao <rohitrao@chromium.org>
Date: Wed Nov 08 00:04:44 2017

[ios] Do nothing if BVC dismissViewController is called more than once.

When the BVC is presented, multiple calls to
|dismissViewControllerAnimated:completion:| end up dismissing the BVC itself.
This is never what we want, so check for this case and return early.

BUG=768563,782338

Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I7a02c9f10fd1c083903beb3b858727276e1d5205
Reviewed-on: https://chromium-review.googlesource.com/757189
Commit-Queue: Rohit Rao (ping after 24h) <rohitrao@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#514664}
[modify] https://crrev.com/a668c02effc76b2dd141a79dd2487a19477396b3/ios/chrome/browser/ui/browser_view_controller.mm