[cr149][Android] Expose didAccountsFetchSucceed method in SigninManager

Chromium changes:
https://chromium.googlesource.com/chromium/src/+/3d631e64797788001eeef6d18db433496fee5fdf

commit 3d631e64797788001eeef6d18db433496fee5fdf
Author: quacksort <quacksort@google.com>
Date:   Tue Apr 28 13:25:24 2026 -0700

    [Signin][Android] Expose didAccountsFetchSucceed method in SigninManager

    This is basically a reland of https://crrev.com/c/7534279, as this
    method was reverted back to private in https://crrev.com/c/7790304.

    This CL also renames the method from didAccountFetchSucceed to
    didAccountsFetchSucceed.

    Fixed: 480076180
    Change-Id: I0003be7ec25eb5fab59ec0b807f76787e511cec6
    Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7797164
    Reviewed-by: Łukasz Barczyński <lbarczynski@google.com>
    Commit-Queue: Lucia Giorgi <quacksort@google.com>
    Reviewed-by: Menghan Yang <myuu@google.com>
    Cr-Commit-Position: refs/heads/main@{#1622000}

browser/signin/services/android/java/src/org/chromium/chrome/browser/signin/services/BraveSigninManager.java

@@ -100,4 +100,9 @@ public class BraveSigninManager implements SigninManager {
 
     @Override
     public void isAccountManaged(CoreAccountInfo account, final Callback<Boolean> callback) {}
+
+    @Override
+    public boolean didAccountsFetchSucceed() {
+        return false;
+    }
 }