Fix unitialized m_cachedHorizontalWritingMode in FloatingObjects.cpp. Failing valgrind layout.

BUG=

Review URL: https://chromiumcodereview.appspot.com/23855009

git-svn-id: svn://svn.chromium.org/blink/trunk@158061 bbb929c8-8fbe-4397-9dbb-9b2b20218538