Switch content tests to use BrowserThreadImpl directly.

content/browser/download/download_id_unittest.cc

Index: content/browser/download/download_id_unittest.cc
diff --git a/content/browser/download/download_id_unittest.cc b/content/browser/download/download_id_unittest.cc
index 2e09525d54b56ef10c2dc00eb7a09649be7ccb53..4078706e02cc888e6ef39c3fa70e6b5e9311050e 100644
--- a/content/browser/download/download_id_unittest.cc
+++ b/content/browser/download/download_id_unittest.cc
@@ -9,11 +9,13 @@
 #include <set>
 #include <vector>
 
+#include "content/browser/browser_thread_impl.h"
 #include "content/browser/download/mock_download_manager.h"
 #include "content/browser/download/mock_download_manager_delegate.h"
-#include "content/test/test_browser_thread.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
+using content::BrowserThreadImpl;
+
 class DownloadIdTest : public testing::Test {
  public:
   DownloadIdTest()
@@ -47,7 +49,7 @@ class DownloadIdTest : public testing::Test {
   scoped_refptr<DownloadManager> download_managers_[2];
   MessageLoopForUI message_loop_;
   // Necessary to delete |DownloadManager|s.
-  content::TestBrowserThread ui_thread_;
+  BrowserThreadImpl ui_thread_;
   size_t num_managers_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadIdTest);