The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9b4aaba68babcfcee3887c04cc5397e6d5755450

commit 9b4aaba68babcfcee3887c04cc5397e6d5755450
Author: tdanderson <tdanderson@chromium.org>
Date: Tue Mar 15 16:59:41 2016

Check for null |tabstrip_| in BrowserView::IsTabStripVisible()

Have BrowserView::IsTabStripVisible() return false
if |tabstrip_| is null, which is consistent with the
behaviour of other BrowserView::Is*Visible() functions.

BUG= 594649 
TEST=none

Review URL: https://codereview.chromium.org/1780333006

Cr-Commit-Position: refs/heads/master@{#381235}

[modify] https://crrev.com/9b4aaba68babcfcee3887c04cc5397e6d5755450/chrome/browser/ui/views/frame/browser_non_client_frame_view_ash.cc
[modify] https://crrev.com/9b4aaba68babcfcee3887c04cc5397e6d5755450/chrome/browser/ui/views/frame/browser_non_client_frame_view_mus.cc
[modify] https://crrev.com/9b4aaba68babcfcee3887c04cc5397e6d5755450/chrome/browser/ui/views/frame/browser_view.cc