[Signin][Android] Disable sign-in promos if MobileIdentityConsistency is on

Adds to SigninManager.isSigninSupported a check for
MobileIdentityConsistency feature to hide sign-in UI surfaces if the
feature is enabled.

Bug: 968140
Change-Id: I39156d4baf852d65117380bf98a983830d61dd6f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1645308
Auto-Submit: Boris Sazonov <bsazonov@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Commit-Queue: Boris Sazonov <bsazonov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666349}

chrome/android/java/src/org/chromium/chrome/browser/signin/SigninManager.java

@@ -27,6 +27,7 @@ import org.chromium.base.annotations.NativeMethods;
 import org.chromium.base.metrics.RecordHistogram;
 import org.chromium.base.metrics.RecordUserAction;
 import org.chromium.base.task.PostTask;
+import org.chromium.chrome.browser.ChromeFeatureList;
 import org.chromium.components.signin.AccountIdProvider;
 import org.chromium.components.signin.AccountManagerFacade;
 import org.chromium.components.signin.AccountTrackerService;
@@ -301,7 +302,8 @@ public class SigninManager implements AccountTrackerService.OnSystemAccountsSeed
      */
     public boolean isSigninSupported() {
         return !ApiCompatibilityUtils.isDemoUser(mContext)
-                && mDelegate.isGooglePlayServicesPresent(mContext);
+                && mDelegate.isGooglePlayServicesPresent(mContext)
+                && !ChromeFeatureList.isEnabled(ChromeFeatureList.MOBILE_IDENTITY_CONSISTENCY);
     }
 
     /**