refactor shortening code

autoload/airline/extensions/branch.vim

@@ -162,9 +162,7 @@ function! airline#extensions#branch#head()
   if empty(b:airline_head) || !found_fugitive_head && !s:check_in_path()
     let b:airline_head = ''
   endif
-  if winwidth(0) < 120 && len(split(b:airline_head, '\zs')) > 9
+  let b:airline_head = airline#util#shorten(b:airline_head, 120, 9)
-    let b:airline_head =  matchstr(b:airline_head, '^.\{9\}').'…'
-  endif
   return b:airline_head
 endfunction
 

autoload/airline/extensions/whitespace.vim

@@ -106,12 +106,7 @@ function! airline#extensions#whitespace#check()
       endif
     endif
   endif
-  if winwidth(0) < 120 && len(split(b:airline_whitespace_check, '\zs')) > 9
+  return airline#util#shorten(b:airline_whitespace_check, 120, 9)
-    return matchstr(b:airline_whitespace_check, '^.\{9\}').'…'
-  else
-    return b:airline_whitespace_check
-  endif
-
 endfunction
 
 function! airline#extensions#whitespace#toggle()

autoload/airline/util.vim

@@ -4,6 +4,14 @@
 call airline#init#bootstrap()
 let s:spc = g:airline_symbols.space
 
+function! airline#util#shorten(text, winwidth, minwidth)
+  if winwidth(0) < a:winwidth && len(split(a:text, '\zs')) > a:minwidth
+    return matchstr(a:text, '^.\{'.a:minwidth.'}').'…'
+  else
+    return a:text
+  endif
+endfunction
+
 function! airline#util#wrap(text, minwidth)
   if a:minwidth > 0 && winwidth(0) < a:minwidth
     return ''