Revert "Revert "HULK SMASH! We've gotta declare REL.""

This reverts commit 30bb1d09eb.

Reason for revert: b/191191441

Bug: 171506470
Bug: 191191441
Change-Id: I698709a27f3b09e5e02143efd7a71157b5ecf75a

core/java/android/app/PendingIntent.java

@@ -365,6 +365,7 @@ public final class PendingIntent implements Parcelable {
         }
 
         if (Compatibility.isChangeEnabled(PENDING_INTENT_EXPLICIT_MUTABILITY_REQUIRED)
+                && !"com.google.android.apps.gcs".equals(packageName)
                 && !flagImmutableSet && !flagMutableSet) {
             String msg = packageName + ": Targeting S+ (version " + Build.VERSION_CODES.S
                     + " and above) requires that one of FLAG_IMMUTABLE or FLAG_MUTABLE"