Add joinable option to SimpleThread::Options as was just done for Thread.

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 30f787b1c4fc02d1436bd23b404c88f107739aca..d3fcb0c58a608228d294866d9071e0074d420662 100644
--- a/base/threading/thread_restrictions.h
+++ b/base/threading/thread_restrictions.h
@@ -9,6 +9,11 @@
 #include "base/logging.h"
 #include "base/macros.h"
 
+#if DCHECK_IS_ON()
+// For DelegateSimpleThread::Delegate.
+#include "base/threading/simple_thread.h"
+#endif
+
 class BrowserProcessImpl;
 class HistogramSynchronizer;
 class NativeBackendKWallet;
@@ -209,6 +214,10 @@ class BASE_EXPORT ThreadRestrictions {
   friend class ui::CommandBufferClientImpl;
   friend class ui::CommandBufferLocal;
   friend class ui::GpuState;
+  // Only required for DCHECK assertions.
+#if DCHECK_IS_ON()
+  friend class DelegateSimpleThread::Delegate;
+#endif
 
   // END ALLOWED USAGE.
   // BEGIN USAGE THAT NEEDS TO BE FIXED.