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

content/test/BUILD.gn

Index: content/test/BUILD.gn
diff --git a/content/test/BUILD.gn b/content/test/BUILD.gn
index 0864192380047792f02a1f6a18f742af5430d6a1..2a08f1709b2f75c2bcac710f02f4d0f81998a1a0 100644
--- a/content/test/BUILD.gn
+++ b/content/test/BUILD.gn
@@ -462,6 +462,7 @@ static_library("browsertest_support") {
 
 mojom("content_test_mojo_bindings") {
   sources = [
+    "../public/test/power_monitor_test.mojom",
     "../public/test/test_service.mojom",
     "test_browser_associated_interfaces.mojom",
   ]
@@ -664,6 +665,7 @@ test("content_browsertests") {
     "../browser/pointer_lock_browsertest.cc",
     "../browser/pointer_lock_browsertest.h",
     "../browser/pointer_lock_browsertest_mac.mm",
+    "../browser/power_monitor_browsertest.cc",
     "../browser/presentation/presentation_browsertest.cc",
     "../browser/renderer_host/input/composited_scrolling_browsertest.cc",
     "../browser/renderer_host/input/interaction_mq_dynamic_browsertest.cc",