Quicken some layout tests doing string concat.

In these tests, a string over 10k characters is assigned to textarea in splitting 
about 10 characters per loop!

In fact, the textarea is not related to test itself.
It seems for a 'debug' purpose at that time.
This files were created in 2009 and I think that we don't need the textarea
 anymore.

BUG=

Review URL: https://codereview.chromium.org/398643005

git-svn-id: svn://svn.chromium.org/blink/trunk@178628 bbb929c8-8fbe-4397-9dbb-9b2b20218538