Plumb site engagement to the renderer process.

content/public/app/mojo/content_renderer_manifest.json

 {
   "name": "content_renderer",
   "display_name": "Content (renderer process)",
   "interface_provider_specs": {
     "service_manager:connector": {
       "provides": {
         "browser": [
           "content::mojom::EmbeddedWorkerInstanceClient",
           "content::mojom::EmbeddedWorkerSetup",
           "content::mojom::FrameFactory",
@@ skipping 11 matching lines @@
         "ui": [
           "discardable_memory",
           "gpu_client"
         ]
       }
     },
     "navigation:frame": {
       "provides": {
         "browser": [
           "blink::mojom::AppBannerController",
+          "blink::mojom::EngagementClient",
           "blink::mojom::InstallationService",
           "content::mojom::ImageDownloader",
           "mojom::MediaDevicesListener"
         ]
       },
       "requires": {
         "content_browser": [ "renderer" ]
       }
     }
   }
 }