I'm looking for a tool that allows me to easily re-wrap text (i.e. remove line breaks, but not paragraph breaks from a text selection or a text field), and that works in my browser (Chrome) and on Windows.

Bonus points for anything that works outside the browser, and that works in-place (i.e. that doesn't require copy-pasting the text through a separate window or using something like http://www.textfixer.com/tools/remove-line-breaks.php)

Browser extensions, GreaseMonkey scripts or applications that also work on Linux and/or Mac (or even better, that are multi-platform) are all welcomed.

Here is an example of how the tool should behave. If I have the following in a text field:

This is a test for SuperUser.com. This is 
a test for SuperUser.com. This is
a test for
SuperUser.com. This is a test 
for SuperUser.com 

This is a test for SuperUser.com. This is 
a test for SuperUser.com. This 
is
a 
test
for SuperUser.com. This is a test for SuperUser.com

I'd like to be able to, for example, select the text, and, with a keyboard shortcut, convert it to:

This is a test for SuperUser.com. This is a test for SuperUser.com. This a test for SuperUser.com. This is a test for SuperUser.com

This is a test for SuperUser.com. This is a test for SuperUser.com. This a test for SuperUser.com. This is a test for SuperUser.com

Thanks in advance!