Change ClipboardMus to use mojo::SyncCallRestrictions::ScopedAllowSyncCall.

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 0c50416c92a41abb7de7433f6de82933cd72738d..90d8433192c39902a87f45e605aed7cdc9ea2184 100644
--- a/base/threading/thread_restrictions.h
+++ b/base/threading/thread_restrictions.h
@@ -83,7 +83,6 @@ class WindowResizeHelperMac;
 }
 
 namespace views {
-class ClipboardMus;
 class ScreenMus;
 }
 
@@ -238,10 +237,6 @@ class BASE_EXPORT ThreadRestrictions {
 #if !defined(OFFICIAL_BUILD)
   friend class content::SoftwareOutputDeviceMus;  // Interim non-production code
 #endif
-  // In the non-mus case, we called blocking OS functions in the ui::Clipboard
-  // implementation which weren't caught by threading restrictions. Our
-  // blocking calls to mus, however, are.
-  friend class views::ClipboardMus;
   friend class views::ScreenMus;
 // END USAGE THAT NEEDS TO BE FIXED.