Remove redundant call of argsList->current() from loops in CSSParser

while loops in CSSParser call argList->current() function at the start
of each iteration, but this is redundant because argsList->next() at
the end of the iteration calls the argList->current() and returns the
result.

BUG=

Review URL: https://chromiumcodereview.appspot.com/21678003

git-svn-id: svn://svn.chromium.org/blink/trunk@155402 bbb929c8-8fbe-4397-9dbb-9b2b20218538