Assert LayoutBlockFlow::GetOffsetMapping() called in layout clean

This patch add |CHECK(!NeedsLayout()| to |LayoutBlockFlow::GetOffsetMapping()|
to stop when it is called with dirty layout instead of causing use-after-tree.

Note: This patch isn't actual fix of http://crbug.com/952718 because we're not
sure why |LayoutBlockFlow::GetOffsetMapping()| is called with dirty layout tree.

Bug: 952718
Change-Id: I9af4a764dbe3899158e8a22cf82b6d92c03a24e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1578148
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653101}
1 file changed