Ignore spaces when determining the length of text to treat as a first-letter pseudo-element.

Spaces are are neither in the Ps, Pe, Pi, Pf and Po sections of UNICODE, so they should not be
considered when determining the length of the first-letter pseudo-element. This change will make
Blink inconsistent with WebKit (which consider spaces, without it being specified by the CSS spec.
It will make Blink consistent with other engines such Trident (IE11) and Opera.

R=eae@chromium.org, tkent@chromium.org
BUG=340688
TEST=Update existing test to treat spaces according to this change, and move it to use reftests.

Review URL: https://codereview.chromium.org/198013006

git-svn-id: svn://svn.chromium.org/blink/trunk@169547 bbb929c8-8fbe-4397-9dbb-9b2b20218538