Update unit tests for BluetoothDevice::GetPrimaryServicesByUUID() etc.

device/bluetooth/bluetooth_device.cc

Index: device/bluetooth/bluetooth_device.cc
diff --git a/device/bluetooth/bluetooth_device.cc b/device/bluetooth/bluetooth_device.cc
index 665cbb685a68da5afedd3e6cdd60dd8898597fff..1820fe464bc979ab177c332e8c06d2690639b2ee 100644
--- a/device/bluetooth/bluetooth_device.cc
+++ b/device/bluetooth/bluetooth_device.cc
@@ -490,12 +490,14 @@ BluetoothDevice::GetDescriptorsByUUID(
     device::BluetoothRemoteGattCharacteristic* characteristic,
     const BluetoothUUID& descriptor_uuid) {
   std::vector<device::BluetoothRemoteGattDescriptor*> descriptors;
-  DVLOG(1) << "Looking for descriptor: " << descriptor_uuid.canonical_value();
-  for (auto* descriptor : characteristic->GetDescriptors()) {
-    DVLOG(1) << "Descriptor in cache: "
-             << descriptor->GetUUID().canonical_value();
-    if (descriptor->GetUUID() == descriptor_uuid) {
-      descriptors.push_back(descriptor);
+  if (characteristic) {
+    DVLOG(1) << "Looking for descriptor: " << descriptor_uuid.canonical_value();
+    for (auto* descriptor : characteristic->GetDescriptors()) {
+      DVLOG(1) << "Descriptor in cache: "
+               << descriptor->GetUUID().canonical_value();
+      if (descriptor->GetUUID() == descriptor_uuid) {
+        descriptors.push_back(descriptor);
+      }
     }
   }
   return descriptors;