GitLab

As per WebContents::SetUserAgentOverride documentation navigation
entries need to be updated to allow user agent override.

Bug: b:175857659
Test: cast_shell_browsertests
Change-Id: Ic829c5130451d2afa4eda598b535c65997a458f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2627883Reviewed-by: Ryan Daum <rdaum@chromium.org>
Commit-Queue: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843633}