Pref service: enable for user prefs in chrome behind a flag.

mojo/public/cpp/bindings/sync_call_restrictions.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_SYNC_CALL_RESTRICTIONS_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_SYNC_CALL_RESTRICTIONS_H_
 
 #include "base/macros.h"
 #include "base/threading/thread_restrictions.h"
 #include "mojo/public/cpp/bindings/bindings_export.h"
 
 #if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON))
 #define ENABLE_SYNC_CALL_RESTRICTIONS 1
 #else
 #define ENABLE_SYNC_CALL_RESTRICTIONS 0
 #endif
 
 namespace leveldb {
 class LevelDBMojoProxy;
 }
 
+namespace prefs {
+class PersistentPrefStoreClient;
+}
+
 namespace ui {
 class Gpu;
 }
 
 namespace views {
 class ClipboardMus;
 }
 
 namespace mojo {
 
@@ skipping 19 matching lines @@
   // Inline the empty definitions of functions so that they can be compiled out.
   static void AssertSyncCallAllowed() {}
 #endif
 
  private:
   // DO NOT ADD ANY OTHER FRIEND STATEMENTS, talk to mojo/OWNERS first.
   // BEGIN ALLOWED USAGE.
   friend class ui::Gpu;  // http://crbug.com/620058
   // LevelDBMojoProxy makes same-process sync calls from the DB thread.
   friend class leveldb::LevelDBMojoProxy;
+  // Pref service connection is sync at startup.
+  friend class prefs::PersistentPrefStoreClient;
+
   // END ALLOWED USAGE.
 
   // BEGIN USAGE THAT NEEDS TO BE FIXED.
   // In the non-mus case, we called blocking OS functions in the ui::Clipboard
   // implementation which weren't caught by sync call restrictions. Our blocking
   // calls to mus, however, are.
   friend class views::ClipboardMus;
   // END USAGE THAT NEEDS TO BE FIXED.
 
 #if ENABLE_SYNC_CALL_RESTRICTIONS
@@ skipping 21 matching lines @@
 
     DISALLOW_COPY_AND_ASSIGN(ScopedAllowSyncCall);
   };
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(SyncCallRestrictions);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_SYNC_CALL_RESTRICTIONS_H_