How to change DPI in Ubuntu GNOME 14.04?

What I would like to do is "Change DPI to 144 in Ubuntu GNOME 14.04".

Because it's first time to me to use linux, I installed VMware Player in my laptop,and I installed Ubuntu GNOME 14.04.
My laptop has 1920x1080 in 11.6 inch display, so I use 144 dpi for Windows 8.1 which is host of VMware, but in Ubuntu GNOME, letters become really small.

At first, I have tried to use Gnome-Tweak-Tool to change the text scaling factor. It changes font sizes in title bars, menus, etc, but not for some application's content. (e.g. firefox)

So, I use MSN to google the other way, and it tells me that in GNOME, dpi size is written in the source code of gnome-setting-deamon.

plugins/xsettings/gsd-xsettings-manager.c
#define DPI_FALLBACK 96

Thus I have tried the commands bellow.

$ mkdir source$ cd source$ apt-get source gnome-settings-deamon$ cd gnome-settings-daemon-3.8.6.1

and replace the row to #define DPI_FALLBACK 144.

What should I do next to reflect to this change for my system?

I'm not sure that I have a collect way or not, so if it's wrong, please tell me the right way.

Thanks for your help.