MacPWAs: Disable new close behavior

The Chat PWA is not receiving notifications or badge updates when no
tabs are open. This may be an issue with Chrome or somewhere in Chat.
The result is that the Chat PWA runs, but does not update the dock icon
on new messages coming in, which is a negative user experience.

Bug: 1080729
Change-Id: I230ae8041bda448d865ccb48ad4980a1846ed617
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2504576
Commit-Queue: ccameron <ccameron@chromium.org>
Commit-Queue: Daniel Murphy <dmurph@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821532}

chrome/common/chrome_features.cc

@@ -83,7 +83,7 @@ const base::Feature kAppShimRemoteCocoa{"AppShimRemoteCocoa",
 // all windows for an app leaves the app running.
 // https://crbug.com/1080729
 const base::Feature kAppShimNewCloseBehavior{"AppShimNewCloseBehavior",
-                                             base::FEATURE_ENABLED_BY_DEFAULT};
+                                             base::FEATURE_DISABLED_BY_DEFAULT};
 #endif  // defined(OS_MAC)
 
 // Enables the built-in DNS resolver.