cheets: implement cros side of WallpaperManagerService.

components/arc/common/arc_bridge.mojom

Index: components/arc/common/arc_bridge.mojom
diff --git a/components/arc/common/arc_bridge.mojom b/components/arc/common/arc_bridge.mojom
index 17b1c3b5e10067dbfc6ec038f5efca0aa5246624..8b19a9781c3441bf8b442c280fe5e4dcd8668fd0 100644
--- a/components/arc/common/arc_bridge.mojom
+++ b/components/arc/common/arc_bridge.mojom
@@ -25,10 +25,11 @@ import "process.mojom";
 import "storage_manager.mojom";
 import "tts.mojom";
 import "video.mojom";
+import "wallpaper.mojom";
 
-// Next MinVersion: 18
+// Next MinVersion: 19
 // Deprecated method IDs: 101, 105
-// Next method ID: 124
+// Next method ID: 125
 interface ArcBridgeHost {
   // Keep the entries alphabetical. In order to do so without breaking
   // compatibility with the ARC instance, explicitly assign each interface a
@@ -100,6 +101,9 @@ interface ArcBridgeHost {
 
   // Notifies Chrome that the VideoInstance interface is ready.
   [MinVersion=6] OnVideoInstanceReady@107(VideoInstance instance_ptr);
+
+  // Notifies Chrome that the WallpaperInstance interface is ready.
+  [MinVersion=18] OnWallpaperInstanceReady@124(WallpaperInstance instance_ptr);
 };
 
 interface ArcBridgeInstance {