add g:clang_format#auto_format

Author: rhysd

plugin/clang_format.vim

@@ -12,4 +12,11 @@ command! -range=% -nargs=0 ClangFormat call clang_format#replace(<line1>, <line2
 
 command! -range=% -nargs=0 ClangFormatEchoFormattedCode echo clang_format#format(<line1>, <line2>)
 
+if 1 || get(g:, 'clang_format#auto_format', 0)
+    augroup plugin-clang-format-auto-format
+        autocmd!
+        autocmd BufWritePre * if &ft ==# 'cpp' | call clang_format#replace(1, line('$')) | endif
+    augroup END
+endif
+
 let g:loaded_clang_format = 1