Move default StyleBuilderFunctions handlers from StyleBuilder.cpp to StyleBuilderFunctions.cpp

Some of the StyleBuilderFunctions handlers were being defined in
StyleBuilder.cpp. This patch cleans moves them to the correct place and
makes some minor clean-ups inside (removing the unused condition check
and a redundant isPrimitiveValue check).

Review URL: https://codereview.chromium.org/236763002

git-svn-id: svn://svn.chromium.org/blink/trunk@171443 bbb929c8-8fbe-4397-9dbb-9b2b20218538