Allow BrowserTestBase to do wait.

base/threading/thread_restrictions.h

Index: base/threading/thread_restrictions.h
diff --git a/base/threading/thread_restrictions.h b/base/threading/thread_restrictions.h
index 248c46f6e677d2bf704521f92e5e2d06438fb4c8..51cfa27a056b530215432a5d6ff85625f93cf7c0 100644
--- a/base/threading/thread_restrictions.h
+++ b/base/threading/thread_restrictions.h
@@ -42,6 +42,7 @@ class Predictor;
 }
 namespace content {
 class BrowserGpuChannelHostFactory;
+class BrowserTestBase;
 class GLHelper;
 class GpuChannelHost;
 class RenderWidgetHelper;
@@ -169,6 +170,7 @@ class BASE_EXPORT ThreadRestrictions {
  private:
   // DO NOT ADD ANY OTHER FRIEND STATEMENTS, talk to jam or brettw first.
   // BEGIN ALLOWED USAGE.
+  friend class content::BrowserTestBase;
   friend class content::RenderWidgetHelper;
   friend class ::HistogramSynchronizer;
   friend class ::ScopedAllowWaitForLegacyWebViewApi;