[Doodle] Allow overriding the API URL via a fieldtrial param

chrome/browser/doodle/doodle_service_factory.cc

 // Copyright 2017 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/doodle/doodle_service_factory.h"
 
 #include <memory>
 #include <utility>
 
 #include "base/memory/ptr_util.h"
+#include "base/metrics/field_trial_params.h"
 #include "base/time/default_clock.h"
 #include "base/time/default_tick_clock.h"
 #include "base/timer/timer.h"
 #include "chrome/browser/google/google_url_tracker_factory.h"
 #include "chrome/browser/profiles/profile.h"
 #include "components/doodle/doodle_fetcher.h"
 #include "components/doodle/doodle_fetcher_impl.h"
 #include "components/doodle/doodle_service.h"
 #include "components/keyed_service/content/browser_context_dependency_manager.h"
 #include "components/prefs/pref_service.h"
 #include "components/safe_json/safe_json_parser.h"
 
 #if defined(OS_ANDROID)
 #include "chrome/browser/android/chrome_feature_list.h"
 #endif
 
+#if defined(OS_ANDROID)
+namespace {
+const char kOverrideUrlParam[] = "doodle_override_url";
+}  // namespace
+#endif
+
 // static
 DoodleServiceFactory* DoodleServiceFactory::GetInstance() {
   return base::Singleton<DoodleServiceFactory>::get();
 }
 
 // static
 doodle::DoodleService* DoodleServiceFactory::GetForProfile(Profile* profile) {
   return static_cast<doodle::DoodleService*>(
       GetInstance()->GetServiceForBrowserContext(profile, /*create=*/true));
 }
 
 DoodleServiceFactory::DoodleServiceFactory()
     : BrowserContextKeyedServiceFactory(
           "DoodleService",
           BrowserContextDependencyManager::GetInstance()) {
   DependsOn(GoogleURLTrackerFactory::GetInstance());
 }
 
 DoodleServiceFactory::~DoodleServiceFactory() = default;
 
 KeyedService* DoodleServiceFactory::BuildServiceInstanceFor(
     content::BrowserContext* context) const {
   Profile* profile = static_cast<Profile*>(context);
   // We don't show doodles in incognito profiles (for now?).
   DCHECK(!profile->IsOffTheRecord());
 
   bool use_gray_background = false;
+  base::Optional<std::string> override_url;
+
 #if defined(OS_ANDROID)
+  DCHECK(base::FeatureList::IsEnabled(chrome::android::kUseNewDoodleApi));
+
   use_gray_background =
       !base::FeatureList::IsEnabled(chrome::android::kChromeHomeFeature);
+
+  std::string override_url_str = base::GetFieldTrialParamValueByFeature(
+      chrome::android::kUseNewDoodleApi, kOverrideUrlParam);
+  // GetFieldTrialParamValueByFeature returns an empty string if the param is
+  // not set.
+  if (!override_url_str.empty()) {
+    override_url = override_url_str;
+  }
 #endif
+
   auto fetcher = base::MakeUnique<doodle::DoodleFetcherImpl>(
       profile->GetRequestContext(),
       GoogleURLTrackerFactory::GetForProfile(profile),
-      base::Bind(&safe_json::SafeJsonParser::Parse), use_gray_background);
+      base::Bind(&safe_json::SafeJsonParser::Parse), use_gray_background,
+      override_url);
   return new doodle::DoodleService(
       profile->GetPrefs(), std::move(fetcher),
       base::MakeUnique<base::OneShotTimer>(),
       base::MakeUnique<base::DefaultClock>(),
       base::MakeUnique<base::DefaultTickClock>(),
       /*override_min_refresh_interval=*/base::nullopt);
 }