Use isSpaceOrNewline rather than its implementation

These two if statements use the isSpaceOrNewline implementation but it is clearer and safer to call the inlined method instead.

Review URL: https://codereview.chromium.org/133273021

git-svn-id: svn://svn.chromium.org/blink/trunk@165283 bbb929c8-8fbe-4397-9dbb-9b2b20218538