DevTools: Network Panel: update "Record Network Log" button title according to state.

Title should reflect action that will happen when button is pressed.

BUG=414140

Review URL: https://codereview.chromium.org/632253002

git-svn-id: svn://svn.chromium.org/blink/trunk@183649 bbb929c8-8fbe-4397-9dbb-9b2b20218538