[fsp] Remove weak pointers from loggers wherever possible.

Crashing is better than ignoring an unexpected callback call.
This patch removes weak pointers from loggers, which used to prevent catching
such bugs.

TEST=unit_test: *FileSystemProvider*
BUG=248427

Review URL: https://codereview.chromium.org/365583003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@281009 0039d316-1c4b-4281-b951-d872f2087c98
7 files changed