[fsp] Rename file_system_name to display_name for consistency.

On the JS side, the argument is called displayName, so on C++ side it should
be display_name for consistency.

TBR=nkostylev@chromium.org
TEST=Not related. Refactoring only.
BUG=248427

Review URL: https://codereview.chromium.org/375793003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@281717 0039d316-1c4b-4281-b951-d872f2087c98
16 files changed