PASSED Manual Testing following the steps in the comment of Igor.

Fixed on:
Tomcat 7.0 + MySQL 5. Portal 6.1.x EE GIT ID: 14d8add6237bc38a42e06d41b4797945405596bf.
Tomcat 7.0 + MySQL 5. Portal 6.2.x GIT ID: aba3f72fdf43645b428ae8ebc2157873a5492d2d.

Sprite images folder should be not empty.

Anyhow, I made a fix that does not required any modification to server.xml. All you have to do is to enable sprite.root.dir. When enabled, sprite images folder will be not empty.

So the whole testing steps are 1-3.

The test should be different: sprites images folder should only contain sprites, and not other theme files.

1. create a folder c:/sprite

2. add sprite.root.dir=c:/sprite to portal-ext.properties

3. start the portal

4. icons are missing (delete browser cache)

5. shut down the server

6. add following lines to: liferay/bundles/tomcat-7.0.27/conf/server.xml:

   (see attached file as an example)

7. restart the server and clear browser cache

Icons should be visible now, and sprite images folder should be not empty.

FAILED Manual Testing using the following steps:
1. Create a folder D:/sprite;
2. Add "sprite.root.dir= D:/sprite" to portal-ext.properties;
3. Start the portal;
After I clear the cache of browser, the icons were missing.
4. Shut down the server;
5. Add
"<Context path="/html/icons" docBase=" D:/sprite/html/icons" />
<Context path="/html/themes/classic" docBase=" D:/sprite/html/themes/classic" />
<Context path="/html/themes/control_panel" docBase=" D:/sprite/html/themes/control_panel" />"
to D:\testingwork\new-trunk\apache-tomcat-7.0.23\conf\server.xml;
6. Copy everything from
LIFERAY-HOME\apache-tomcat-7.0.23\webapps\ROOT\html\icons to D:/sprite/html/icons and
LIFERAY-HOME\apache-tomcat-7.0.23\apache-tomcat-7.0.23\webapps\ROOT\html\themes\classic to D:/sprite/html/themes/classic
LIFERAY-HOME\apache-tomcat-7.0.23\apache-tomcat-7.0.23\webapps\ROOT\html\themes\control_panel to D:/sprite/html/themes/control_panel
7. Restart the server and clear the cache.

Reproduced on:
Tomcat 7.0.19 + MySQL 5. 6.1.x Revision: 86200.
There is nothing in D:/sprite.

Failed on:
Tomcat 7.0.23 + MySQL 5. 6.1.x Revision: 95060.
I also cannot see any icons.