Make createFragmentFromText() to check preserve newline more carefully

This patch changes createFragmentFromText() to check preserve newline from renderer of first node in range or start container of range.

When textarea created by script and setting its value to only a newline, shadow DOM tree of this textarea contains empty text node in first child. This empty text node doesn't have associated renderer and createFragmentFromText() used this empty text node for checking preserving newline.

This empty text node is created by HTMLElement::setInnerText(), which also uses renderer for checking preserving newline, for dynamically created textarea not inserted document, doesn't have associated renderer.

BUG=268148
R=tkent@chromium.org

Review URL: https://codereview.chromium.org/22395002

git-svn-id: svn://svn.chromium.org/blink/trunk@155646 bbb929c8-8fbe-4397-9dbb-9b2b20218538