[mus]Add FrameGenerator::SetHighContrastMode(bool)

services/ui/ws/window_server.cc

Index: services/ui/ws/window_server.cc
diff --git a/services/ui/ws/window_server.cc b/services/ui/ws/window_server.cc
index a1a67187ffb9ada208d3a6b522edd8f6c0aed92e..192f754d20796ce58949ef07b049159965e0da0e 100644
--- a/services/ui/ws/window_server.cc
+++ b/services/ui/ws/window_server.cc
@@ -285,6 +285,12 @@ void WindowServer::SetHighContrastMode(const UserId& user, bool enabled) {
   if (IsUserInHighContrastMode(user) == enabled)
     return;
   high_contrast_mode_[user] = enabled;
+
+  if (user == user_id_tracker_.active_id()) {
+    // Propagate the change to all Displays so that FrameGenerators start
+    // requesting BeginFrames.
+    display_manager_->SetHighContrastMode(enabled);
+  }
 }
 
 uint32_t WindowServer::GenerateWindowManagerChangeId(