Move transformationForTextBox() call out of the fragment-loop

textBox is invariant, so no need to fetch and check the transform for each
fragment.

Review URL: https://codereview.chromium.org/362923007

git-svn-id: svn://svn.chromium.org/blink/trunk@177517 bbb929c8-8fbe-4397-9dbb-9b2b20218538