Make ForwardingDisplayDelegate initially sync.

ui/display/mojo/native_display_delegate.mojom

 // Copyright 2017 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.
 
 module display.mojom;
 
 import "ui/display/mojo/display_constants.mojom";
 import "ui/display/mojo/display_mode.mojom";
 import "ui/display/mojo/display_snapshot_mojo.mojom";
 import "ui/display/mojo/gamma_ramp_rgb_entry.mojom";
 import "ui/gfx/geometry/mojo/geometry.mojom";
 
 // Corresponds to display::NativeDisplayObserver.
 interface NativeDisplayObserver {
   OnConfigurationChanged();
 };
 
 // Corresponds to display::NativeDisplayDelegate. This only implements
 // functionality that is used by Ozone DRM.
 interface NativeDisplayDelegate {
-  // Initializes and registers the observer.
-  Initialize(NativeDisplayObserver observer);
+  // Initializes and registers the observer. This is synchronous so that ash
+  // initialization has an initial set of displays to use.
+  [Sync]
+  Initialize(NativeDisplayObserver observer) => (array<DisplaySnapshotMojo> snapshots);
 
   // Take control of the displays from any other controlling process.
   TakeDisplayControl() => (bool result);
 
   // Let others control the displays.
   RelinquishDisplayControl() => (bool result);
 
   // Queries for a list of fresh displays.
   GetDisplays() => (array<DisplaySnapshotMojo> snapshots);
 
   // Configures the display represented by |display_id| to use |mode| and
   // positions the display to |origin| in the framebuffer. |mode| can be null,
   // which represents disabling the display.
   Configure(int64 display_id,
             DisplayMode mode,
             gfx.mojom.Point origin) => (bool status);
 
   // Gets HDCP state of output.
   GetHDCPState(int64 display_id) => (bool status, HDCPState state);
 
   // Sets HDCP state of output.
   SetHDCPState(int64 display_id, HDCPState state) => (bool status);
 
   // Set the gamma tables and correction matrix for |display_id|.
   SetColorCorrection(int64 display_id,
                      array<GammaRampRGBEntry> degamma_lut,
                      array<GammaRampRGBEntry> gamma_lut,
                      array<float> correction_matrix);
 };