Rewrite download manager unit to be actual unit tests.

content/browser/browser_context.cc

Index: content/browser/browser_context.cc
diff --git a/content/browser/browser_context.cc b/content/browser/browser_context.cc
index 17e60d969b96ff3774345e9e3d40ba8d139e4d36..9814a1936b71699cd2ca3d40b5bfccc162e68cc6 100644
--- a/content/browser/browser_context.cc
+++ b/content/browser/browser_context.cc
@@ -75,7 +75,7 @@ void CreateQuotaManagerAndClients(BrowserContext* context) {
       context->GetPath(), context->IsOffTheRecord(),
       context->GetSpecialStoragePolicy(), quota_manager->proxy(),
       BrowserThread::GetMessageLoopProxyForThread(BrowserThread::FILE));
-  context->SetUserData(kDatabaseTrackerKeyName, 
+  context->SetUserData(kDatabaseTrackerKeyName,
                        new UserDataAdapter<DatabaseTracker>(db_tracker));
 
   FilePath path = context->IsOffTheRecord() ? FilePath() : context->GetPath();
@@ -142,8 +142,8 @@ DOMStorageContextImpl* GetDOMStorageContextImpl(BrowserContext* context) {
 DownloadManager* BrowserContext::GetDownloadManager(
     BrowserContext* context) {
   if (!context->GetUserData(kDownloadManagerKeyName)) {
-    scoped_refptr<DownloadManager> download_manager = new DownloadManagerImpl(
-        GetContentClient()->browser()->GetNetLog());
+    scoped_refptr<DownloadManager> download_manager =
+        DownloadManagerImpl::Create(GetContentClient()->browser()->GetNetLog());
     context->SetUserData(
         kDownloadManagerKeyName,
         new UserDataAdapter<DownloadManager>(download_manager));