[Mac] Change linebreak on paste in Omnibox.
Omnibox can't have linebreaks, so the code stripped them so that
pasted wrapped URLs worked. That breaks pasted search text, such as
street addresses, so convert newlines to spaces if there is other
whitespace present.
Also convert OmniboxViewMac code to use Omnibox version of
GetClipboardText(), so that the code can be cross-platform.
BUG=51971
TEST=See bug.
Review URL: https://chromiumcodereview.appspot.com/
10534149
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@143090 0039d316-1c4b-4281-b951-d872f2087c98