Change AccountManagerHelper initialization

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

Index: components/signin/core/browser/android/java/src/org/chromium/components/signin/AccountManagerHelper.java
diff --git a/components/signin/core/browser/android/java/src/org/chromium/components/signin/AccountManagerHelper.java b/components/signin/core/browser/android/java/src/org/chromium/components/signin/AccountManagerHelper.java
index 761a7286a6f89a379e34daaf3ae9e8980950a86b..e5f42bfd9eb1d50221a69596130492d09231090e 100644
--- a/components/signin/core/browser/android/java/src/org/chromium/components/signin/AccountManagerHelper.java
+++ b/components/signin/core/browser/android/java/src/org/chromium/components/signin/AccountManagerHelper.java
@@ -7,7 +7,6 @@ package org.chromium.components.signin;
 import android.accounts.Account;
 import android.accounts.AuthenticatorDescription;
 import android.app.Activity;
-import android.content.Context;
 import android.os.AsyncTask;
 import android.support.annotation.Nullable;
 
@@ -44,7 +43,12 @@ public class AccountManagerHelper {
     @VisibleForTesting
     public static final String FEATURE_IS_CHILD_ACCOUNT_KEY = "service_uca";
 
-    private static final AtomicReference<AccountManagerHelper> sInstance = new AtomicReference<>();
+    private static final AtomicReference<AccountManagerHelper> sAtomicInstance =
+            new AtomicReference<>();
+
+    private static final Object sLock = new Object();
+    private static Throwable sInstanceInitializedBy;
+    private static Throwable sTestingInstanceInitializedBy;
 
     private final AccountManagerDelegate mDelegate;
 
@@ -76,51 +80,61 @@ public class AccountManagerHelper {
     }
 
     /**
-     * Initialize AccountManagerHelper with a custom AccountManagerDelegate.
-     * Ensures that the singleton AccountManagerHelper hasn't been created yet.
-     * This can be overriden in tests using the overrideAccountManagerHelperForTests method.
+     * Initialize AccountManagerHelper with a custom AccountManagerDelegate. Ensures that it wasn't
+     * already initialized.
+     * Tests can override this, see {@link #overrideAccountManagerHelperForTests}.
      *
      * @param delegate the custom AccountManagerDelegate to use.
+     *
+     * @see #overrideAccountManagerHelperForTests
      */
     public static void initializeAccountManagerHelper(AccountManagerDelegate delegate) {
-        if (!sInstance.compareAndSet(null, new AccountManagerHelper(delegate))) {
-            throw new IllegalStateException("AccountManagerHelper is already initialized!");
+        assert delegate != null;
+        synchronized (sLock) {
+            if (sInstanceInitializedBy != null) {
+                throw new IllegalStateException(
+                        "AccountManagerHelper is already initialized.", sInstanceInitializedBy);
+            }
+            sInstanceInitializedBy = new Throwable();
+            if (sTestingInstanceInitializedBy != null) return;
+            sAtomicInstance.set(new AccountManagerHelper(delegate));
         }
     }
 
     /**
-     * Singleton instance getter. Singleton must be initialized before calling this
-     * (by initializeAccountManagerHelper or overrideAccountManagerHelperForTests).
-     *
-     * @return a singleton instance
-     */
-    public static AccountManagerHelper get() {
-        AccountManagerHelper instance = sInstance.get();
-        assert instance != null : "AccountManagerHelper is not initialized!";
-        return instance;
-    }
-
-    /**
-     * Override AccountManagerHelper with a custom AccountManagerDelegate in tests.
-     * Unlike initializeAccountManagerHelper, this will override the existing instance of
-     * AccountManagerHelper if any. Only for use in Tests.
+     * Override AccountManagerHelper with a custom AccountManagerDelegate for tests. Only for use
+     * in tests. This should be called before call to {@link #initializeAccountManagerHelper}
+     * to make sure instance returned by {@link #get} doesn't change on the fly.
      *
-     * @param context the applicationContext is retrieved from the context used as an argument.
      * @param delegate the custom AccountManagerDelegate to use.
      */
     @VisibleForTesting
-    public static void overrideAccountManagerHelperForTests(
-            Context context, AccountManagerDelegate delegate) {
-        sInstance.set(new AccountManagerHelper(delegate));
+    public static void overrideAccountManagerHelperForTests(AccountManagerDelegate delegate) {
+        assert delegate != null;
+        synchronized (sLock) {
+            Throwable initializedBy = sInstanceInitializedBy != null
+                    ? sInstanceInitializedBy
+                    : sTestingInstanceInitializedBy;
+            if (initializedBy != null) {
+                throw new IllegalStateException(
+                        "AccountManagerHelper is already initialized.", initializedBy);
+            }
+            sTestingInstanceInitializedBy = new Throwable();
+            sAtomicInstance.set(new AccountManagerHelper(delegate));
+        }
     }
 
     /**
-     * Resets custom AccountManagerHelper set with {@link #overrideAccountManagerHelperForTests}.
-     * Only for use in Tests.
+     * Singleton instance getter. Singleton must be initialized before calling this
+     * (by initializeAccountManagerHelper or overrideAccountManagerHelperForTests).
+     * It is guaranteed that this method always returns the same instance during app lifetime.
+     *
+     * @return a singleton instance
      */
-    @VisibleForTesting
-    public static void resetAccountManagerHelperForTests() {
-        sInstance.set(null);
+    public static AccountManagerHelper get() {
+        AccountManagerHelper instance = sAtomicInstance.get();
+        assert instance != null : "AccountManagerHelper is not initialized!";
+        return instance;
     }
 
     /**