CSS Tokenizer: Fix edge cases in number parsing

This patch fixes a couple of small issues in the css-syntax number
parsing routine:

1) We shouldn't consume a "." if the next character isn't a digit
2) If any exponent argument is present we should use a 'number'
type (in the code we just check if we consumed anything after the
integer portion)

http://dev.w3.org/csswg/css-syntax/#consume-number

BUG=424988

Review URL: https://codereview.chromium.org/662343002

git-svn-id: svn://svn.chromium.org/blink/trunk@183979 bbb929c8-8fbe-4397-9dbb-9b2b20218538