Reland "desktop-pwas: Add more tests for opening desktop pwas"

Prerender is turned off in release builds and turned on via Finch
for some users. This patch turns it on for the relevant test.

This is a reland of d643999c63e8a30ca6d1a6ecca6da2d356197e3d
Original change's description:
> desktop-pwas: Add more tests for opening desktop pwas
> 
> Tests for:
> 
> 1. POST and GET forms
> 2. Prerender links
> 3. Fetch requests
> 4. Open link in incognito"
> 5. Navigating inside an incognito window
> 
> Bug: 
> Change-Id: Icb383ee64b5d0e253dcf507e56cea718affab99d
> Reviewed-on: https://chromium-review.googlesource.com/661998
> Reviewed-by: Matt Giuca <[email protected]>
> Reviewed-by: Istiaque Ahmed <[email protected]>
> Commit-Queue: Giovanni Ortuño Urquidi <[email protected]>
> Cr-Commit-Position: refs/heads/master@{#504506}

[email protected], [email protected]

Change-Id: Idf37c9a399ba8bc082804d2760e321ca875e411c
Reviewed-on: https://chromium-review.googlesource.com/688115
Reviewed-by: Giovanni Ortuño Urquidi <[email protected]>
Commit-Queue: Giovanni Ortuño Urquidi <[email protected]>
Cr-Commit-Position: refs/heads/master@{#504918}
1 file changed