[SVG2] Allow leading and trailing whitespace in svg attributes using
<integer>, <angle>, <number>, <length> and <percentage>.

BUG=377503,339899

Review URL: https://codereview.chromium.org/302643004

git-svn-id: svn://svn.chromium.org/blink/trunk@175574 bbb929c8-8fbe-4397-9dbb-9b2b20218538