Reland of Reimplement AccountManagerHelper singleton instance creation

components/signin/core/browser/android/java/src/org/chromium/components/signin/ChildAccountInfoFetcher.java

Index: components/signin/core/browser/android/java/src/org/chromium/components/signin/ChildAccountInfoFetcher.java
diff --git a/components/signin/core/browser/android/java/src/org/chromium/components/signin/ChildAccountInfoFetcher.java b/components/signin/core/browser/android/java/src/org/chromium/components/signin/ChildAccountInfoFetcher.java
index b2e8ae19d8cb63222b649b251ee2cf3f4382099e..42969b7d6abb7dd90b16484d23ee06ca05dbf58e 100644
--- a/components/signin/core/browser/android/java/src/org/chromium/components/signin/ChildAccountInfoFetcher.java
+++ b/components/signin/core/browser/android/java/src/org/chromium/components/signin/ChildAccountInfoFetcher.java
@@ -89,6 +89,13 @@ public final class ChildAccountInfoFetcher {
         nativeSetIsChildAccount(mNativeAccountFetcherService, mAccountId, isChildAccount);
     }
 
+    @CalledByNative
+    private static void initializeForTests() {
+        Context context = ContextUtils.getApplicationContext();
+        AccountManagerDelegate delegate = new SystemAccountManagerDelegate();
+        AccountManagerHelper.overrideAccountManagerHelperForTests(context, delegate);
+    }
+
     private static native void nativeSetIsChildAccount(
             long accountFetcherServicePtr, String accountId, boolean isChildAccount);
 }