A fractional value of the css letter-spacing property is not rendered as expected

https://bugs.webkit.org/show_bug.cgi?id=20606

Reviewed by Simon Fraser.

Source/WebCore:

This turns on fractional letter-spacing and word-spacing CSS values.
It is taken mostly from Blink r153727 and iOS. Updating the relevant
types is all that is necessary

* css/DeprecatedStyleBuilder.cpp:
(WebCore::DeprecatedStyleBuilder::DeprecatedStyleBuilder):
* page/animation/CSSPropertyAnimation.cpp:
(WebCore::CSSPropertyAnimationWrapperMap::CSSPropertyAnimationWrapperMap):
* platform/graphics/Font.cpp:
(WebCore::Font::Font):
(WebCore::Font::width):
* platform/graphics/Font.h:
(WebCore::Font::wordSpacing):
(WebCore::Font::letterSpacing):
(WebCore::Font::setWordSpacing):
(WebCore::Font::setLetterSpacing):
* rendering/style/RenderStyle.cpp:
(WebCore::RenderStyle::wordSpacing):
(WebCore::RenderStyle::letterSpacing):
(WebCore::RenderStyle::setWordSpacing):
(WebCore::RenderStyle::setLetterSpacing):
* rendering/style/RenderStyle.h:

Change-Id: I49cedbf555426f3fae3fe58ec4eb25569d358997
git-svn-id: http://svn.webkit.org/repository/webkit/trunk@161521 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@digia.com>