Remove TreatNullAs=NullString for CSS*Rule

http://dev.w3.org/csswg/cssom/#csscharsetrule
http://dev.w3.org/csswg/css-animations/#csskeyframesrule
http://dev.w3.org/csswg/cssom/#csspagerule
http://dev.w3.org/csswg/cssom/#cssrule
http://dev.w3.org/csswg/cssom/#cssstylerule

The tests for the updated properties pass in Firefox Nightly, IE11
Release Preview and Opera 12.16, with these exceptions:

Firefox reflects CSSCharsetRule.encoding, CSSKeyframesRule.name, and
CSSPageRule.selectorText as null, and ignores setting
CSSStyleRule.selectorText.

IE doesn't support CSSCharsetRule, throws an exception when setting
CSSPageRule.selectorText and ignores setting
CSSStyleRule.selectorText.

Opera throws an exception when setting CSSRule.cssText, ignores
setting CSSCharsetRule.encoding and throws an exception when setting
CSSPageRule.selectorText.

This is not very impressive, but since there is no attribute for which
all the other browsers agree, just going with the spec seems sound.

BUG=310298

Review URL: https://codereview.chromium.org/107313004

git-svn-id: svn://svn.chromium.org/blink/trunk@163424 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add pointer-events="bounding-box" for svg content.

The 'bounding-box' keyword in 'pointer-events' enables
svg authors to leave out certain invisible 'hit-area'
elements, and instead get them generated based on the
bounding box. This is convenient for example if one wants
multiline text in svg to respond to mouse events over the
entire region it covers. Another common use-case is
groups, which are container elements. These elements
currently are not possible to target directly, since
they only get events through bubbling from their
children.

This patch makes container elements targetable if one
specifies 'pointer-events: bounding-box' on them (either
as an svg presentation attribute or in css).

The 'bounding-box' keyword is specified in SVG2, 
https://svgwg.org/svg2-draft/interact.html#PointerEventsProp. 

Note: The keyword was called 'boundingbox' in SVG Tiny 1.2,
http://www.w3.org/TR/SVGTiny12/interact.html#PointerEventsProperty,
but it was renamed to be more in sync with CSS syntax in general.

R=pdr
BUG=

Review URL: https://codereview.chromium.org/45733010

git-svn-id: svn://svn.chromium.org/blink/trunk@163425 bbb929c8-8fbe-4397-9dbb-9b2b20218538