Update libchromiumcontent

* vendor/libchromiumcontent cf87e4d...3944c1c (1):
  > Compile and export SQLitePersistentCookieStore
Persist cookies to disk

We use Chrome's SQLitePersistentCookieStore to save cookies to a file called
"Cookies" within the application support directory.

Fixes #5.
Fix lifetime management of URLRequestContextGetter

I noticed this bug while adding persistent cookie storage.
Fix double-delete of BrowserMainParts

The caller of BrowserClient::CreateBrowserMainParts handles destroying the
BrowserMainParts instance we return.