Optimize named property access on CSSStyleDeclaration objects

Optimize named property access on CSSStyleDeclaration objects

When reading property on a CSSStyleDeclaration object, the property name
is transformed into a possible CSS property name and looked up as such.
This transformation involves copying the property name to a StringBuilder
while converting from camelCase to dash-separated.

Positive matches are cached in a local static hash map, but negative
matches were not.  A script reading properties like "getPropertyValue"
would trigger the conversion to "get-property-value" and CSS property
lookup every time.

Optimize by caching negative matches as well as positive ones.

BUG=

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170490

[Jens Widell, 2014-03-31 10:41:36]

Found while investigating why a random site triggered lots of realloc() calls;
turned out to be the shrink-to-fit reallocation of the StringBuilder buffer used
in this code, when massaging the property name "getPropertyValue" over and over.

The added performance test (which is essentially a copy of the
CSSPropertySetterGetter.html test) runs approximately 25 % faster for me with
this fix.

[abarth-chromium, 2014-03-31 21:02:18]

lgtm

[abarth-chromium, 2014-03-31 21:02:26]

The CQ bit was checked by abarth@chromium.org

[commit-bot: I haz the power, 2014-03-31 21:02:33]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jl@opera.com/219153002/1

[commit-bot: I haz the power, 2014-04-01 00:00:29]

Change committed as 170490