Document WebView DevTools Crashes UI.

Bug: 1058571
Test: tools/md_browser/md_browser.py
Test: Upload to gerrit > open file > click "gitiles"
Change-Id: I1e8948fb94585402c156503cef06b92732587626
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2142215
Commit-Queue: Hazem Ashmawy <hazems@chromium.org>
Reviewed-by: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758879}