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Ensure that we log the winning display mode from the manifest
accounting for display_override.

To test the change use: chrome --enable-features=WebAppManifestDisplayOverride
Example websites:
 https://mwjacksonmsft.github.io/pwa/display-override-custom/index.html
 (display == browser, display_override == [standard])

Image of chrome://histograms
https://imgur.com/a/aVzadhf

Explainer: https://github.com/WICG/display-override/blob/master/explainer.m
Design document: https://docs.google.com/document/d/1hEmbGVHMN38q1YTaaGccQ-Y5CHr7xIURYPRWXTuvZLo/edit?usp=sharing
I2P: https://groups.google.com/a/chromium.org/d/topic/blink-dev/WvIeZT8uSzw/discussion

Bug: 1109520
Change-Id: Ie401fd770eae262c9ad6d7e76e3d7e21d6a285c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2354531Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Commit-Queue: Mike Jackson <mjackson@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#797862}