Properly ifdef sync code in password_manager

Fix one misplaced header include and use PASSWORD_MANAGER_ENABLE_SYNC
macro to properly guard the other place of sync usage to fix a linking
issue when PASSWORD_MANAGER_ENABLE_SYNC is disabled.

Review URL: https://codereview.chromium.org/943533002

Cr-Commit-Position: refs/heads/master@{#317043}
2 files changed