[sync] WebContentsObserver based sessions notifications

chrome/browser/sync/sessions/sync_sessions_web_contents_router_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/sync/sessions/sync_sessions_web_contents_router_factory.h"
+
+#include "base/logging.h"
+#include "base/memory/singleton.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/sync/sessions/sync_sessions_web_contents_router.h"
+#if !defined(OS_ANDROID)
+#include "chrome/browser/sync/sessions/sync_sessions_multi_windowed_web_contents_router.h"
+#endif  // !defined(OS_ANDROID)
+
+#include "components/keyed_service/content/browser_context_dependency_manager.h"
+
+namespace sync_sessions {
+
+// static
+SyncSessionsWebContentsRouter*
+SyncSessionsWebContentsRouterFactory::GetForProfile(Profile* profile) {
+  return static_cast<SyncSessionsWebContentsRouter*>(
+      GetInstance()->GetServiceForBrowserContext(profile, true));
+}
+
+// static
+SyncSessionsWebContentsRouterFactory*
+SyncSessionsWebContentsRouterFactory::GetInstance() {
+  return base::Singleton<SyncSessionsWebContentsRouterFactory>::get();
+}
+
+SyncSessionsWebContentsRouterFactory::SyncSessionsWebContentsRouterFactory()
+    : BrowserContextKeyedServiceFactory(
+          "SyncSessionsWebContentsRouter",
+          BrowserContextDependencyManager::GetInstance()) {}
+
+SyncSessionsWebContentsRouterFactory::~SyncSessionsWebContentsRouterFactory() {}
+
+KeyedService* SyncSessionsWebContentsRouterFactory::BuildServiceInstanceFor(
+    content::BrowserContext* context) const {
+#if !defined(OS_ANDROID)

[Nicolas Zea, 2017/03/20 18:14:50]

nit: prefer have the positive version of the conditional be the initial (e.g. if
android do this, else do that). Having negation just adds a tiny bit of
cognitive load without really providing any benefit.

[Patrick Noland, 2017/03/21 22:54:31]

With composition, this seemed no longer possible without having an empty #ifdef
block followed by an #else, which I figured was even more cognitive load than
negation. 

+  return new SyncSessionsMultiWindowedWebContentsRouter(
+      static_cast<Profile*>(context));
+#else
+  return new SyncSessionsWebContentsRouter(static_cast<Profile*>(context));
+#endif  // !defined(OS_ANDROID)
+}
+
+}  // namespace sync_sessions