[NTP::Cleanup] Avoid nested complex function calls

chrome/browser/ntp_snippets/content_suggestions_service_factory.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ntp_snippets/content_suggestions_service_factory.h"
 
 #include <utility>
 
 #include "base/feature_list.h"
 #include "base/files/file_path.h"
@@ skipping 151 matching lines @@
       content::BrowserContext::GetDefaultStoragePartition(profile)
           ->GetURLRequestContext();
 
   base::FilePath database_dir(
       profile->GetPath().Append(ntp_snippets::kDatabaseFolder));
   scoped_refptr<base::SequencedTaskRunner> task_runner =
       BrowserThread::GetBlockingPool()
           ->GetSequencedTaskRunnerWithShutdownBehavior(
               base::SequencedWorkerPool::GetSequenceToken(),
               base::SequencedWorkerPool::CONTINUE_ON_SHUTDOWN);
-  bool is_stable_channel =
-      chrome::GetChannel() == version_info::Channel::STABLE;
-  auto provider = base::MakeUnique<RemoteSuggestionsProviderImpl>(
-      service, pref_service, g_browser_process->GetApplicationLocale(),
-      service->category_ranker(),
-      base::MakeUnique<RemoteSuggestionsFetcher>(
-          signin_manager, token_service, request_context, pref_service,
-          language_model, base::Bind(&safe_json::SafeJsonParser::Parse),
-          is_stable_channel ? google_apis::GetAPIKey()
-                            : google_apis::GetNonStableAPIKey(),
-          service->user_classifier()),
-      base::MakeUnique<ImageFetcherImpl>(base::MakeUnique<ImageDecoderImpl>(),
-                                         request_context.get()),
-      base::MakeUnique<ImageDecoderImpl>(),
-      base::MakeUnique<RemoteSuggestionsDatabase>(database_dir, task_runner),
-      base::MakeUnique<RemoteSuggestionsStatusService>(signin_manager,
-                                                       pref_service));
+
+  std::unique_ptr<RemoteSuggestionsProviderImpl> provider;
+  {

[tschumann, 2017/02/01 15:07:59]

sorry for the late response. I'm not a fan of such scopes. They usually only
cure a symptom, not the underlying problem. Usually, the better answer for
reducing scope is to extract a function but there are a lot of variables to
pass.

I'd be in favor of the change that only moves 'suggestions_fetcher' into a
separate variable and leaves the rest unchanged. The original problem stemmed
from the long parameter list of the fetcher's constructor which might got
confused with the provider's constructor. So let's just fix that and keep the
rest.

+    bool is_stable_channel =
+        chrome::GetChannel() == version_info::Channel::STABLE;
+    auto suggestions_fetcher = base::MakeUnique<RemoteSuggestionsFetcher>(
+        signin_manager, token_service, request_context, pref_service,
+        language_model, base::Bind(&safe_json::SafeJsonParser::Parse),
+        is_stable_channel ? google_apis::GetAPIKey()
+                          : google_apis::GetNonStableAPIKey(),
+        service->user_classifier());
+    auto image_fetcher = base::MakeUnique<ImageFetcherImpl>(
+        base::MakeUnique<ImageDecoderImpl>(), request_context.get());
+    auto database =
+        base::MakeUnique<RemoteSuggestionsDatabase>(database_dir, task_runner);
+    auto status_service = base::MakeUnique<RemoteSuggestionsStatusService>(
+        signin_manager, pref_service);
+    provider = base::MakeUnique<RemoteSuggestionsProviderImpl>(
+        service, pref_service, g_browser_process->GetApplicationLocale(),
+        service->category_ranker(), std::move(suggestions_fetcher),
+        std::move(image_fetcher), base::MakeUnique<ImageDecoderImpl>(),
+        std::move(database), std::move(status_service));
+  }
 
   PersistentScheduler* scheduler = nullptr;
 #if defined(OS_ANDROID)
   scheduler = NTPSnippetsLauncher::Get();
 #endif  // OS_ANDROID
 
   auto scheduling_provider =
       base::MakeUnique<SchedulingRemoteSuggestionsProvider>(
           service, std::move(provider), scheduler, service->user_classifier(),
           pref_service, base::MakeUnique<base::DefaultClock>());
@@ skipping 124 matching lines @@
                             language_model, pref_service, profile);
   }
 
   if (base::FeatureList::IsEnabled(
           ntp_snippets::kForeignSessionsSuggestionsFeature)) {
     RegisterForeignSessionsProvider(sync_service, service, pref_service);
   }
 
   return service;
 }