Add TestBrowserThreadBundle into RenderViewHostTestHarness. Kill some unnecessary real threads.

components/web_modal/web_contents_modal_dialog_manager_unittest.cc

Index: components/web_modal/web_contents_modal_dialog_manager_unittest.cc
diff --git a/components/web_modal/web_contents_modal_dialog_manager_unittest.cc b/components/web_modal/web_contents_modal_dialog_manager_unittest.cc
index 613182bdb592f6d0d269181a20dfe519e40bab5e..5f01c147b6f6f5dc8c5d741ab2df620e37eb72a6 100644
--- a/components/web_modal/web_contents_modal_dialog_manager_unittest.cc
+++ b/components/web_modal/web_contents_modal_dialog_manager_unittest.cc
@@ -4,7 +4,6 @@
 
 #include "components/web_modal/native_web_contents_modal_dialog_manager.h"
 #include "components/web_modal/web_contents_modal_dialog_manager.h"
-#include "content/public/test/test_browser_thread.h"
 #include "content/public/test/test_renderer_host.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -15,17 +14,10 @@ namespace web_modal {
 class WebContentsModalDialogManagerTest
     : public content::RenderViewHostTestHarness {
  public:
-  WebContentsModalDialogManagerTest()
-      : ui_thread_(BrowserThread::UI, &message_loop_) {
-  }
-
   virtual void SetUp() {
     content::RenderViewHostTestHarness::SetUp();
     WebContentsModalDialogManager::CreateForWebContents(web_contents());
   }
-
- private:
-  content::TestBrowserThread ui_thread_;
 };
 
 class NativeWebContentsModalDialogManagerCloseTest