WebApp: Enable DesktopPWAsUnifiedInstall feature by default.

It disables BookmarkAppInstallManager code path (with BookmarkAppHelper inside).
It enables unified WebAppInstallManager and InstallFinalizer infrastructure.

Bug: 915043
Change-Id: Id77289a7b6b51681b8833d9c83d7a9657c1af624
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1627847
Commit-Queue: Alexey Baskakov <loyso@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670335}

chrome/common/chrome_features.cc

@@ -224,7 +224,7 @@ const base::Feature kDesktopPWAsWithoutExtensions{
 // Enables or disables new Desktop PWAs unified |InstallManager| that does not
 // use extensions.
 const base::Feature kDesktopPWAsUnifiedInstall{
-    "DesktopPWAsUnifiedInstall", base::FEATURE_DISABLED_BY_DEFAULT};
+    "DesktopPWAsUnifiedInstall", base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Enables or disables the ability to install PWAs from the omnibox.
 const base::Feature kDesktopPWAsOmniboxInstall{