[DeviceService] Add end-to-end browsertest for PowerMonitor

content/shell/browser/content_shell_renderer_manifest_overlay.json

 {
   "name": "content_renderer",
   "interface_provider_specs": {
     "service_manager:connector": {
       "provides": {
         "browser": [
+          "content::mojom::PowerMonitorTest",
           "content::mojom::TestService"
         ]
       }
     },
     "navigation:frame": {
       "provides": {
         "browser": [
           "content::mojom::LayoutTestControl"
         ]
       }
     }
   }
 }