GitLab

In incognito mode, we shouldn't write to the metadata cache.
BrowserContext::GetPath() will return the path of the normal
profile in incognito mode.

BUG=778425

Change-Id: If1cd5d819d0b754010f60f776226c34d92e383f4
Reviewed-on: https://chromium-review.googlesource.com/1033540Reviewed-by: Xing Liu <xingliu@chromium.org>
Commit-Queue: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#554554}