Ensure only one IdentityManagerFactory instance gets created

IdentityManagerFactory is a class meant to be instantiated in the
browser process via base::Singleton, thus it's not expected to have
several instance of them.

However, since PR #7480[1] we're actually creating two instances for
Brave: the BraveIdentityManagerFactory (subclass) instanced from
ProfileSyncServiceFactory as part of a DependsOn() statement, and
another one for every other place in the code (68 callpoints at this
time) using DependsOn(IdentityManagerFactory::GetInstance()) to
initialize different services.

This hasn't rang any alarm until Chromium 92.0.4496.3, but in that
release some changes were made[2] including the introduction of the
IdentityManagerProvider class, which now DCHECKs for having only
one instance of IdentityManagerFactory created in the browser:

  void SetIdentityManagerProvider(const IdentityManagerProvider& provider) {
    IdentityManagerProvider& instance = GetIdentityManagerProvider();
    DCHECK(!instance);
    instance = provider;
  }

...meaning that we will get a crash on startup and all the unit and
browser tests crashing on DCHECK-enabled builds, revealing this issue
that we didn't know we had until now.

This patch, makes changes to ensure we have one IdentityManagerFactory
instance only, by removing a few parts of the infrastructure added with
PR #7480[1] and simply leveraging chromium_src overrides to implement
the changes we need for the IdentityManager: to empty implementations
of GetAccountsInCookieJar() and GetPrimaryAccountMutator().

[1] #7480
[2] https://chromium-review.googlesource.com/c/chromium/src/+/2824129

Resolves brave/brave-browser#15659

browser/sources.gni

@@ -19,7 +19,6 @@ import("//brave/browser/ipfs/sources.gni")
 import("//brave/browser/new_tab/sources.gni")
 import("//brave/browser/permissions/sources.gni")
 import("//brave/browser/search_engines/sources.gni")
-import("//brave/browser/signin/sources.gni")
 import("//brave/browser/speedreader/sources.gni")
 import("//brave/browser/themes/sources.gni")
 import("//brave/chromium_src/chrome/browser/prefs/sources.gni")
@@ -318,7 +317,6 @@ brave_chrome_browser_sources += brave_browser_ipfs_sources
 brave_chrome_browser_sources += brave_browser_new_tab_sources
 brave_chrome_browser_sources += brave_browser_permissions_sources
 brave_chrome_browser_sources += brave_browser_search_engines_sources
-brave_chrome_browser_sources += brave_browser_signin_sources
 brave_chrome_browser_sources += brave_browser_speedreader_sources
 brave_chrome_browser_sources += brave_browser_themes_sources
 brave_chrome_browser_sources += brave_browser_wallet_sources
@@ -338,7 +336,6 @@ brave_chrome_browser_deps += brave_browser_ipfs_deps
 brave_chrome_browser_deps += brave_browser_new_tab_deps
 brave_chrome_browser_deps += brave_browser_permissions_deps
 brave_chrome_browser_deps += brave_browser_search_engines_deps
-brave_chrome_browser_deps += brave_browser_signin_deps
 brave_chrome_browser_deps += brave_browser_speedreader_deps
 brave_chrome_browser_deps += brave_browser_themes_deps
 brave_chrome_browser_deps += brave_browser_wallet_deps

chromium_src/chrome/browser/sync/profile_sync_service_factory.cc

@@ -3,14 +3,10 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-#include "brave/browser/signin/brave_identity_manager_factory.h"
 #include "brave/browser/sync/brave_profile_sync_service_delegate.h"
-#include "brave/components/signin/public/identity_manager/brave_identity_manager.h"
 #include "brave/components/sync/driver/brave_sync_profile_sync_service.h"
 #include "chrome/browser/sync/device_info_sync_service_factory.h"
 
-#define IdentityManagerFactory BraveIdentityManagerFactory
-
 #define BRAVE_BUILD_SERVICE_INSTANCE_FOR                         \
   std::make_unique<syncer::BraveProfileSyncService>(             \
       std::move(init_params),                                    \
@@ -20,5 +16,3 @@
 #include "../../../../../chrome/browser/sync/profile_sync_service_factory.cc"
 
 #undef BRAVE_BUILD_SERVICE_INSTANCE_FOR
-
-#undef IdentityManagerFactory

chromium_src/components/signin/public/identity_manager/identity_manager.cc

@@ -0,0 +1,24 @@
+/* Copyright (c) 2021 The Brave Authors. All rights reserved.
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "brave/chromium_src/components/signin/public/identity_manager/identity_manager.h"
+
+#include <utility>
+#include <vector>
+
+#define GetAccountsInCookieJar GetAccountsInCookieJar_Unused
+#include "../../../../../../components/signin/public/identity_manager/identity_manager.cc"
+#undef GetAccountsInCookieJar
+
+namespace signin {
+
+AccountsInCookieJarInfo IdentityManager::GetAccountsInCookieJar() const {
+  // accounts_in_cookie_jar_info.accounts_are_fresh must be false,
+  // see `ProfileSyncService::OnEngineInitialized`
+  return AccountsInCookieJarInfo(false, std::vector<gaia::ListedAccount>(),
+                                 std::vector<gaia::ListedAccount>());
+}
+
+}  // namespace signin

chromium_src/components/signin/public/identity_manager/identity_manager.h

@@ -6,7 +6,9 @@
 #ifndef BRAVE_CHROMIUM_SRC_COMPONENTS_SIGNIN_PUBLIC_IDENTITY_MANAGER_IDENTITY_MANAGER_H_
 #define BRAVE_CHROMIUM_SRC_COMPONENTS_SIGNIN_PUBLIC_IDENTITY_MANAGER_IDENTITY_MANAGER_H_
 
-#define GetAccountsInCookieJar virtual GetAccountsInCookieJar
+#define GetAccountsInCookieJar           \
+  GetAccountsInCookieJar_Unused() const; \
+  AccountsInCookieJarInfo GetAccountsInCookieJar
 
 #include "../../../../../../components/signin/public/identity_manager/identity_manager.h"
 

chromium_src/components/signin/public/identity_manager/identity_manager_builder.cc

@@ -3,19 +3,24 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+#define BuildIdentityManager BuildIdentityManager_Unused
+#define BuildIdentityManagerInitParameters \
+  BuildIdentityManagerInitParameters_ChromiumImpl
 #include "../../../../../../components/signin/public/identity_manager/identity_manager_builder.cc"
+#undef BuildIdentityManagerInitParameters
+#undef BuildIdentityManager
 
 #include "brave/components/signin/internal/identity_manager/brave_primary_account_mutator_impl.h"
-#include "brave/components/signin/public/identity_manager/brave_identity_manager.h"
+#include "components/signin/public/identity_manager/identity_manager.h"
 
 namespace signin {
 
 namespace {
 
-IdentityManager::InitParameters BuildBraveIdentityManagerInitParameters(
+IdentityManager::InitParameters BuildIdentityManagerInitParameters(
     IdentityManagerBuildParams* params) {
   IdentityManager::InitParameters init_params =
-      BuildIdentityManagerInitParameters(params);
+      BuildIdentityManagerInitParameters_ChromiumImpl(params);
 
   init_params.primary_account_mutator =
       std::make_unique<BravePrimaryAccountMutatorImpl>(
@@ -29,10 +34,10 @@ IdentityManager::InitParameters BuildBraveIdentityManagerInitParameters(
 
 }  // namespace
 
-std::unique_ptr<BraveIdentityManager> BuildBraveIdentityManager(
+std::unique_ptr<IdentityManager> BuildIdentityManager(
     IdentityManagerBuildParams* params) {
-  return std::make_unique<BraveIdentityManager>(
-      BuildBraveIdentityManagerInitParameters(params));
+  return std::make_unique<IdentityManager>(
+      BuildIdentityManagerInitParameters(params));
 }
 
 }  // namespace signin