Enable feature PolicyFCMInvalidations by default

The results of rolling out to 1% Stable:
* PolicyInvalidationsRegistrationResult:
    https://screenshot.googleplex.com/pnbpqVwsRU9
* DevicePolicyInvalidations: https://screenshot.googleplex.com/MEWsE7RkOwk
* DevicePolicyRefresh2: https://screenshot.googleplex.com/VWuHQvxsKx3
* PolicyInvalidations: https://screenshot.googleplex.com/EqoY7uBTVO7
* PolicyRefresh2: https://screenshot.googleplex.com/qEXcoLEXziK

The results are as expected.

The issue regarding Klopf-Klopf devices not receiving remote commands
b/141327786 was confirmed that it was not caused by "Invalidation
Service Migration".

Bug: 939039
Change-Id: Idd37c358e7bc9d4a69e204c1a91e6a44c376675b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2014966Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Askar Aitzhan <askaraitzhan@google.com>
Cr-Commit-Position: refs/heads/master@{#734438}

chrome/common/chrome_features.cc

@@ -336,7 +336,7 @@ const base::Feature kDownloadsLocationChange{"DownloadsLocationChange",
 // If enabled, policies will use FCM (Firebase Cloud Messaging) for its
 // invalidations.
 const base::Feature kPolicyFcmInvalidations{"PolicyFCMInvalidations",
-                                            base::FEATURE_DISABLED_BY_DEFAULT};
+                                            base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Disables ambient authentication in incognito mode.
 const base::Feature kEnableAmbientAuthenticationInIncognito{