Implement create attribute API functions for BTLE.

device/bluetooth/bluetooth_adapter_unittest.cc

Index: device/bluetooth/bluetooth_adapter_unittest.cc
diff --git a/device/bluetooth/bluetooth_adapter_unittest.cc b/device/bluetooth/bluetooth_adapter_unittest.cc
index 0c12221a1610dd81fddfdb4e2b01df387524d74b..9533e962b1fb09d1cf7302f56bf46628be29ebc5 100644
--- a/device/bluetooth/bluetooth_adapter_unittest.cc
+++ b/device/bluetooth/bluetooth_adapter_unittest.cc
@@ -103,6 +103,11 @@ class TestBluetoothAdapter : public BluetoothAdapter {
       const CreateAdvertisementCallback& callback,
       const CreateAdvertisementErrorCallback& error_callback) override {}
 
+  BluetoothLocalGattService* GetGattService(
+      const std::string& identifier) const override {
+    return nullptr;
+  }
+
   void TestErrorCallback() {}
 
   ScopedVector<BluetoothDiscoverySession> discovery_sessions_;