Roll cros_system_api and use constants pulled in.

device/bluetooth/dbus/fake_bluetooth_le_advertising_manager_client.cc

Index: device/bluetooth/dbus/fake_bluetooth_le_advertising_manager_client.cc
diff --git a/device/bluetooth/dbus/fake_bluetooth_le_advertising_manager_client.cc b/device/bluetooth/dbus/fake_bluetooth_le_advertising_manager_client.cc
index f40f3d3ec545fa441b2b6fc9cad31f665c2687e6..c7fcf2594c04ab77ae914ec71480f5fcc6ccfc42 100644
--- a/device/bluetooth/dbus/fake_bluetooth_le_advertising_manager_client.cc
+++ b/device/bluetooth/dbus/fake_bluetooth_le_advertising_manager_client.cc
@@ -18,6 +18,8 @@ namespace bluez {
 namespace {
 
 constexpr char kAdvertisingManagerPath[] = "/fake/hci0";
+// According to the Bluetooth spec, these are the min and max values possible
+// for advertising interval. Core 4.2 Spec, Vol 2, Part E, Section 7.8.5.
 constexpr uint16_t kMinIntervalMs = 20;
 constexpr uint16_t kMaxIntervalMs = 10240;