Split BrowserThread into public API and private implementation, step 1.

content/browser/site_instance_unittest.cc

Index: content/browser/site_instance_unittest.cc
diff --git a/content/browser/site_instance_unittest.cc b/content/browser/site_instance_unittest.cc
index 50cc712040a5dd716fb490eeefdf2e33ce1a67ec..d19ef681663475d9270048924d11dc262c7c3113 100644
--- a/content/browser/site_instance_unittest.cc
+++ b/content/browser/site_instance_unittest.cc
@@ -5,7 +5,6 @@
 #include "base/compiler_specific.h"
 #include "base/stl_util.h"
 #include "base/string16.h"
-#include "content/browser/browser_thread.h"
 #include "content/browser/browsing_instance.h"
 #include "content/browser/child_process_security_policy.h"
 #include "content/browser/mock_content_browser_client.h"
@@ -20,6 +19,7 @@
 #include "content/public/common/content_client.h"
 #include "content/public/common/url_constants.h"
 #include "content/test/test_browser_context.h"
+#include "content/test/test_browser_thread.h"
 #include "googleurl/src/url_util.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -115,7 +115,7 @@ class SiteInstanceTest : public testing::Test {
 
  private:
   MessageLoopForUI message_loop_;
-  BrowserThread ui_thread_;
+  content::TestBrowserThread ui_thread_;
 
   SiteInstanceTestBrowserClient browser_client_;
   content::ContentBrowserClient* old_browser_client_;