Add implementation for parsing device info in read/write attribute calls.

device/bluetooth/dbus/bluetooth_gatt_attribute_helpers.cc

Index: device/bluetooth/dbus/bluetooth_gatt_attribute_helpers.cc
diff --git a/device/bluetooth/dbus/bluetooth_gatt_attribute_helpers.cc b/device/bluetooth/dbus/bluetooth_gatt_attribute_helpers.cc
new file mode 100644
index 0000000000000000000000000000000000000000..8cfcb3735057f4f2e53b4562d6363e8e3d80909a
--- /dev/null
+++ b/device/bluetooth/dbus/bluetooth_gatt_attribute_helpers.cc
@@ -0,0 +1,43 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "device/bluetooth/dbus/bluetooth_gatt_attribute_helpers.h"
+
+#include <string>
+
+#include "base/logging.h"
+#include "dbus/message.h"
+#include "dbus/object_path.h"
+
+namespace bluez {
+
+namespace {
+
+constexpr char kDeviceField[] = "device";
+
+}  // namespace
+
+dbus::ObjectPath ReadDevicePath(dbus::MessageReader* reader) {
+  dbus::MessageReader array_reader(nullptr);
+  if (!reader->PopArray(&array_reader))
+    return dbus::ObjectPath();
+
+  // Go through all the keys in the dictionary to find the device key.
+  while (array_reader.HasMoreData()) {
+    dbus::MessageReader dict_entry_reader(nullptr);
+    std::string key;
+    if (!array_reader.PopDictEntry(&dict_entry_reader) ||
+        !dict_entry_reader.PopString(&key)) {
+      return dbus::ObjectPath();
+    } else if (key == kDeviceField) {
+      dbus::ObjectPath device_path;
+      dict_entry_reader.PopVariantOfObjectPath(&device_path);
+      return device_path;
+    }
+  }
+
+  return dbus::ObjectPath();
+}
+
+}  // namespace bluez