The behavior of the CSS parser modes wasn't very obvious and many
behavior decisions were made comparing the modes.
    
Now there are methods clarifying a certain behavior which takes
a CSSParserMode and returns true or false. These are now used in
the code instead of comparing the mode directly, making the code
much more clear.
    
This solution was chosen instead of feature flags in order to
avoid growing the CSSParserMode which is packed tightly in the
StylePropertySet.
    
The names of the modes have also been clarified. For instance
the CSSQuirksMode is now called HTMLQuirksMode as it is not a
CSS mode as such. Similarly CSSAttributeMode is now called
HTMLAttributeMode which fits with SVGAttributeMode naming.

Review URL: https://codereview.chromium.org/26952005

git-svn-id: svn://svn.chromium.org/blink/trunk@160210 bbb929c8-8fbe-4397-9dbb-9b2b20218538