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 the current text field that is being edited), and that works at least with text fields 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 have an easy tool that allows me 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!