Decouple Power Monitor from //content.

device/BUILD.gn

Index: device/BUILD.gn
diff --git a/device/BUILD.gn b/device/BUILD.gn
index 7b9c0042eae8952c8044bcc47c8220a531c93442..cb2f90fd7f1cb8dd690aa4cb8cf1a822f536af4f 100644
--- a/device/BUILD.gn
+++ b/device/BUILD.gn
@@ -63,6 +63,8 @@ test("device_unittests") {
     "gamepad/gamepad_provider_unittest.cc",
     "generic_sensor/platform_sensor_and_provider_unittest_win.cc",
     "generic_sensor/platform_sensor_provider_unittest.cc",
+    "power_monitor/power_monitor_message_broadcaster_unittest.cc",
+    "power_monitor/public/cpp/power_monitor_broadcast_source_unittest.cc",
     "test/run_all_unittests.cc",
     "wake_lock/wake_lock_service_context_unittest.cc",
   ]
@@ -80,6 +82,9 @@ test("device_unittests") {
     "//device/generic_sensor",
     "//device/generic_sensor:testing",
     "//device/geolocation:unittests",
+    "//device/power_monitor",
+    "//device/power_monitor/public/cpp",
+    "//device/power_monitor/public/interfaces",
     "//device/power_save_blocker",
     "//device/wake_lock",
     "//mojo/common",