[signin] Fix crash in AccountReconcilor::Lock::~Lock()

The lock can now outlive the AccountReconcilor.

Bug: 923094
Change-Id: I92443549d50354eb1418fe8495dddea5bf310d5d
Reviewed-on: https://chromium-review.googlesource.com/c/1425499
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Commit-Queue: David Roger <droger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625150}
3 files changed