dpwas: Enable display_override flag by default

Turn's on support for display_override.

To test the change use: chrome
Example installable apps:
 https://mwjacksonmsft.github.io/pwa/display-override/index.html
 (display: fullscreen, display_override == [minimal-ui, standalone])
 https://mwjacksonmsft.github.io/pwa/display-override-custom/index.html
 (display == browser, display_override == [standalone])

Example non-installable apps:
 https://mwjacksonmsft.github.io/pwa/display-override-browser/index.html
 (display: fullscreen, display_override == [browser, standalone])

Explainer: https://github.com/WICG/display-override/blob/master/explainer.md
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
I2S: https://groups.google.com/a/chromium.org/g/blink-dev/c/MZgYJgS4Lcs/m/NnUxG2_mAAAJ

Bug: 1092667
Change-Id: I8e77b8e38e05e683173f0820fad7006725be24b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2536210
Commit-Queue: Mike Jackson <mjackson@microsoft.com>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#835729}

content/public/common/content_features.cc

@@ -753,7 +753,7 @@ const base::Feature kV8VmFuture{"V8VmFuture",
 
 // Enable display_override manifest entry for web applications.
 const base::Feature kWebAppManifestDisplayOverride{
-    "WebAppManifestDisplayOverride", base::FEATURE_DISABLED_BY_DEFAULT};
+    "WebAppManifestDisplayOverride", base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Enable window controls overlays for desktop PWAs
 const base::Feature kWebAppWindowControlsOverlay{