[bluetooth] Renamed global variables in device/bluetooth

In jumbo build experiments, files get merged and variables and
functions with the same name may end up in the same namespace/scope
and conflict. This happens for g_singleton in :
bluetooth_adapter_factory.cc
bluetooth_adapter_factory_wrapper.cc

[1] https://chromium.googlesource.com/chromium/src/+/lkgr/docs/jumbo.md

Bug: 887254
Change-Id: I97ff48a6aae71be0b935db1f7623da7ef65bac97
Reviewed-on: https://chromium-review.googlesource.com/c/1325109Reviewed-by: Giovanni Ortuño Urquidi <ortuno@chromium.org>
Commit-Queue: Byoungkwon Ko <codeimpl@gmail.com>
Cr-Commit-Position: refs/heads/master@{#609940}

device/bluetooth/bluetooth_adapter_factory_wrapper.cc

@@ -16,7 +16,7 @@
 namespace {
 
 static base::LazyInstance<device::BluetoothAdapterFactoryWrapper>::Leaky
-    g_singleton = LAZY_INSTANCE_INITIALIZER;
+    g_bluetooth_adapter_factory_wrapper_singleton = LAZY_INSTANCE_INITIALIZER;
 
 }  // namespace
 
@@ -32,7 +32,7 @@ BluetoothAdapterFactoryWrapper::~BluetoothAdapterFactoryWrapper() {
 
 // static
 BluetoothAdapterFactoryWrapper& BluetoothAdapterFactoryWrapper::Get() {
-  return g_singleton.Get();
+  return g_bluetooth_adapter_factory_wrapper_singleton.Get();
 }
 
 bool BluetoothAdapterFactoryWrapper::IsLowEnergySupported() {