viz: Convert a sync api in ServerGpuMemoryBufferManager into async.

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 e9f801778ea0edf81a316d7eeb0a9c436c3cadcd..1ef8d6b1278380783c54e73ff5a41b29b9ef4254 100644
--- a/base/threading/thread_restrictions.h
+++ b/base/threading/thread_restrictions.h
@@ -88,6 +88,10 @@ namespace views {
 class ScreenMus;
 }
 
+namespace viz {
+class ServerGpuMemoryBufferManager;
+}
+
 namespace base {
 
 namespace android {
@@ -238,6 +242,7 @@ class BASE_EXPORT ThreadRestrictions {
   friend class content::SoftwareOutputDeviceMus;  // Interim non-production code
 #endif
   friend class views::ScreenMus;
+  friend class viz::ServerGpuMemoryBufferManager;
 // END USAGE THAT NEEDS TO BE FIXED.
 
 #if DCHECK_IS_ON()