Linux StorageMonitor: Add btrfs as a known file system type.

Review URL: https://codereview.chromium.org/151083003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248143 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248143
Support asynchronous patching operations in the component updater.

First part of a 2-part changelist.
The second part is https://codereview.chromium.org/25909005/

BUG=304879

Review URL: https://codereview.chromium.org/25883006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248144 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248144