It looks semi-related to https://bugs.chromium.org/p/chromium/issues/detail?id=835296 - but that one got fixed in 67, but I am still seeing it in 67.

Unable to reproduce the issue on reported version chrome 67.0.3396.62 using Mac 10.13.3.

Steps:
-----------
1. Enabled multi monitor set up on Mac
2. Launched chrome and moved one tab to second monitor.
3. Disabled the second monitor.
Observed that Chrome UI looks nice and there is no blank.

Cc'ing lgrey@ from  Issue 835296  for more inputs on this.

@reporter: Would it be possible to attach screen-cast of the behavior you are seeing?

I can repro by making the window full height on the external monitor and downloading something (so the download bar is showing).

+sdy@

The root cause here is that DownloadShelf is causing a relayout when the backing store changes (https://cs.chromium.org/chromium/src/chrome/browser/ui/cocoa/download/download_shelf_view_cocoa.mm?sq=package:chromium&dr&g=0&l=147)

This relayout sees the new content view frame and adjusts accordingly

But:

Later in the process of switching screens we see:
	2   AppKit                              0x00007fff4605bf19 -[NSView resizeSubviewsWithOldSize:] + 504
	3   AppKit                              0x00007fff4603a6f6 -[NSView setFrameSize:] + 1672
	4   AppKit                              0x00007fff460d9df9 -[NSWindow _oldPlaceWindow:] + 1006
	5   AppKit                              0x00007fff460d921a -[NSWindow _setFrameCommon:display:stashSize:] + 3108
	6   AppKit                              0x00007fff460d85e9 -[NSWindow _setFrame:display:allowImplicitAnimation:stashSize:] + 222
	7   AppKit                              0x00007fff460d8504 -[NSWindow setFrame:display:] + 67
	8   AppKit                              0x00007fff463529b8 -[NSWindow _adjustWindowToScreen] + 1728

Which adjusts everything as if the previous layout hadn't happened, and so, bumps everything down by Height(oldScreen) - Height(newScreen) 

sdy@ can you think of something less brute force than readjusting the height in this case? We'd need to merge back to 68, so ellyjones@ and I have already rejected trying to work around this some more complex way.

It looks like -viewDidChangeBackingProperties doesn't attempt to lay out anything other than the shelf itself. How does it end up affecting the rest of the window? I'm guessing that commenting it out doesn't help, though?

One quick option I can think of is to make the height *not* depend on the divider height: just size the shelf to `kMDShelfHeight`.

You might also try just doing `self.needsLayout = YES` in -viewDidMoveToWindow and -viewDidChangeBackingProperties, and then putting the actual height adjustment (the body of adjustHeightForDivider) in a -layout override.

Re c#5

	2   libchrome_dll.dylib                 0x000000010998effa -[BrowserWindowController(Private) applyLayout:] + 570
	3   libchrome_dll.dylib                 0x000000010998a6e1 -[BrowserWindowController(Private) layoutSubviews] + 433
	4   libchrome_dll.dylib                 0x000000010997ace1 -[BrowserWindowController resizeView:newHeight:] + 2385
	5   libchrome_dll.dylib                 0x0000000109900ef8 -[AnimatableView setHeight:] + 88
	6   libchrome_dll.dylib                 0x00000001099d1d12 -[DownloadShelfView adjustHeightForDivider] + 306

Magic!

I see :/

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b6a6f344bb8e4279c60f48e02caa7cbef461765b

commit b6a6f344bb8e4279c60f48e02caa7cbef461765b
Author: Leonard Grey <lgrey@chromium.org>
Date: Mon Jun 11 23:00:30 2018

Cocoa: don't adjust download shelf height to account for divider

Making this change during a screen transition causes a browser view
layout. However, AppKit appears to manually adjust subviews of views that
were resized due to a screen change, and does this using the former sizes.
This happens *after* layout is triggered in this case, causing the contents
of the view to be pushed down by the difference in height between displays.

Bug:  850829 
Change-Id: I53a0b03114fa9647c389595265211f5639a523a0
Reviewed-on: https://chromium-review.googlesource.com/1095322
Reviewed-by: Sidney San Martín <sdy@chromium.org>
Commit-Queue: Leonard Grey <lgrey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#566189}
[modify] https://crrev.com/b6a6f344bb8e4279c60f48e02caa7cbef461765b/chrome/browser/ui/cocoa/download/download_shelf_view_cocoa.mm

This bug requires manual review: M68 has already been promoted to the beta branch, so this requires manual review
Please contact the milestone owner if you have questions.
Owners: cmasso@(Android), kariahda@(iOS), bhthompson@(ChromeOS), abdulsyed@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

+abdulsyed@

Abdul, we believe this is a very safe merge

Actually, +govind@, since it looks like Abdul is out

Approving merge to M68 branch 3440 based on comment #12. Please merge. Thank you.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3480b2a11f92e7fcf063ad5a4b1403a91b43413c

commit 3480b2a11f92e7fcf063ad5a4b1403a91b43413c
Author: Leonard Grey <lgrey@chromium.org>
Date: Thu Jun 14 15:06:51 2018

Cocoa: don't adjust download shelf height to account for divider

Making this change during a screen transition causes a browser view
layout. However, AppKit appears to manually adjust subviews of views that
were resized due to a screen change, and does this using the former sizes.
This happens *after* layout is triggered in this case, causing the contents
of the view to be pushed down by the difference in height between displays.

Bug:  850829 
Change-Id: I53a0b03114fa9647c389595265211f5639a523a0
Reviewed-on: https://chromium-review.googlesource.com/1095322
Reviewed-by: Sidney San Martín <sdy@chromium.org>
Commit-Queue: Leonard Grey <lgrey@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#566189}(cherry picked from commit b6a6f344bb8e4279c60f48e02caa7cbef461765b)
Reviewed-on: https://chromium-review.googlesource.com/1101097
Reviewed-by: Leonard Grey <lgrey@chromium.org>
Cr-Commit-Position: refs/branch-heads/3440@{#359}
Cr-Branched-From: 010ddcfda246975d194964ccf20038ebbdec6084-refs/heads/master@{#561733}
[modify] https://crrev.com/3480b2a11f92e7fcf063ad5a4b1403a91b43413c/chrome/browser/ui/cocoa/download/download_shelf_view_cocoa.mm

Issue 845953 has been merged into this issue.

 Issue 856252  has been merged into this issue.

 Issue 864289  has been merged into this issue.

 Issue 873276  has been merged into this issue.