Increase away. It should be 44x44pt (UIKit standard), so if it isn't make it so :)

Load shedding bugs to Ed.

Currently it is 32x32pt. Here is what it will look like with 44x44. (I highlighted it in green so you can see the close button dimensions. 
 
https://drive.google.com/open?id=1Mf41Q3c3uME_dmzuFhAcsZZITy3E-U78

Instead of actually increasing the button and cell header size, let's just use an overlaid tap target button that receives taps for the close icon. This tap target can be 44x44 as recommended.

I am fine keeping it as is as long as the tap target is 44x44. But it means that the middle of the button probably have to be 22 pt from the top and the right.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/60d379e2c7630d1a346b22b10d90ac2cef956690

commit 60d379e2c7630d1a346b22b10d90ac2cef956690
Author: edchin <edchin@chromium.org>
Date: Fri Jun 29 17:42:32 2018

[ios] Make close button tap target larger on tab grid

Since the close button and cell header is smaller than the recommended
tap target, use an overlaid tap target to receive taps for the close
button.

Bug:  842647 
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ibc728aeba89cc9183a5de7d7fe1e8795dc3da99c
Reviewed-on: https://chromium-review.googlesource.com/1118756
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Commit-Queue: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571521}
[modify] https://crrev.com/60d379e2c7630d1a346b22b10d90ac2cef956690/ios/chrome/browser/ui/tab_grid/grid/grid_cell.mm
[modify] https://crrev.com/60d379e2c7630d1a346b22b10d90ac2cef956690/ios/chrome/browser/ui/tab_grid/grid/grid_constants.h
[modify] https://crrev.com/60d379e2c7630d1a346b22b10d90ac2cef956690/ios/chrome/browser/ui/tab_grid/grid/grid_constants.mm

Can this be closed?

Verified on chrome beta version 69.0.3497.58 on iPhone 8 plus and iPad 2018 with iOS 11.4.1.  Could able to easily close tab on 1 tap.  Looks good.