Remove empty directories in LayoutTests/platform.

This is a follow-up to http://crrev.com/22504003,
which was committed as r155898.

TBR=ojan@chromium.org



git-svn-id: svn://svn.chromium.org/blink/trunk@155904 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move all the HAVE() macros related to string manipulations to wtf/StringExtras.h. The goal of this refactoring is to reduce the scope of these macros and only make them visible to files where it is used.

Review URL: https://chromiumcodereview.appspot.com/22118002

git-svn-id: svn://svn.chromium.org/blink/trunk@155905 bbb929c8-8fbe-4397-9dbb-9b2b20218538