Decouple Power Monitor from //content.

device/BUILD.gn

Index: device/BUILD.gn
diff --git a/device/BUILD.gn b/device/BUILD.gn
index 5cb034943d01ddf62ed31cfa1e18372773aa7cfd..b401e6ba3aad0641ce81b598b8c7ae00c993d2ac 100644
--- a/device/BUILD.gn
+++ b/device/BUILD.gn
@@ -62,6 +62,8 @@ test("device_unittests") {
     "bluetooth/test/test_bluetooth_local_gatt_service_delegate.h",
     "gamepad/gamepad_provider_unittest.cc",
     "generic_sensor/platform_sensor_provider_unittest.cc",
+    "power_monitor/power_monitor_broadcast_source_unittest.cc",
+    "power_monitor/power_monitor_message_broadcaster_unittest.cc",
     "test/run_all_unittests.cc",
     "wake_lock/wake_lock_service_context_unittest.cc",
   ]
@@ -79,6 +81,9 @@ test("device_unittests") {
     "//device/generic_sensor",
     "//device/generic_sensor:testing",
     "//device/geolocation:unittests",
+    "//device/power_monitor:power_monitor_broadcast_source",
+    "//device/power_monitor:power_monitor_message_broadcaster",
+    "//device/power_monitor/public/interfaces",
     "//device/power_save_blocker",
     "//device/wake_lock",
     "//mojo/common",