Bouncing to P1 as this is blocking running Bookmarks EG tests on Xcode9/iOS 11.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4e8cac2a96b0553324b2860479084fe84dd0528e

commit 4e8cac2a96b0553324b2860479084fe84dd0528e
Author: sczs <sczs@chromium.org>
Date: Thu Jul 27 17:26:05 2017

[ios] Fix Bookmark text field edit item accessibility

The "X" clear text button was previously not accessible via voice-over, they could only access the
whole cell, because of this users couldn't really tap the X button when using voice over.
Now they can select the Textfield and clear text button separately. 

This CL makes the textField accessible instead of the Cell, as Apple recommends:
https://developer.apple.com/library/content/documentation/UserExperience/Conceptual/iPhoneAccessibility/Making_Application_Accessible/Making_Application_Accessible.html#//apple_ref/doc/uid/TP40008785-CH102-SW3
(We might have to edit other cells in order to make their Subviews accessible) 

Screenshot Before: 
https://drive.google.com/open?id=0Byo6-Nuda2jgcjVlZTNrZmI2cGc

Screenshot After:
https://drive.google.com/open?id=0Byo6-Nuda2jgVzZMYTctTmM1Vnc

Screenshot from Apple Settings (Device):
https://drive.google.com/open?id=0Byo6-Nuda2jgUXZHRGlSLTFUV28

Bug:  747594 
Change-Id: I70394c062227a33f7b7a74228675c2e74385faca
Reviewed-on: https://chromium-review.googlesource.com/583533
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#490009}
[modify] https://crrev.com/4e8cac2a96b0553324b2860479084fe84dd0528e/ios/chrome/browser/ui/bookmarks/cells/bookmark_text_field_item.mm

Checked on the chrome canary version 62.0.3170.0, on iPad Air and iPhone 6 plus with iOS 11 beta, iPad Air and iPhone 6s plus with iOS with iOS 10.3.3.  "x" is accessible and read with voice over : on.