I refer to http://www.google.com/support/forum/p/Chrome/thread?tid=389f306a52817110&hl=en.

Modify (or Add) webkit data structure in following file:

• Windows XP: ..\Documents and Settings\User_Name\Local Settings\Application Data\Google\Chrome\User Data\Default\Preference
• Mac OS X: $HOME/Users/breadncup/Library/Application Support/Google/Chrome/Default/Preference

"webkit": {
 "webprefs": {
 "default_fixed_font_size": 11,
 "default_font_size": 12,
 "fixed_font_family": "Bitstream Vera Sans Mono",
 "minimum_font_size": 12,
 "minimum_logical_font_siz": 12,
 "sansserif_font_family": "Times New Roman",
 "serif_font_family": "Arial",
 "standard_font_is_serif": false,
 "text_areas_are_resizable": true
 }
 }