Out-of-line RenderStyle substructure copying helpers.

Out-of-line RenderStyle substructure copying helpers.
<https://webkit.org/b/126340>

This shrinks the .access() calls by moving memory allocation logic
out-of-line, though I'm really doing this to make Instruments.app
allocations output more readable.

Writes to e.g 'font' or 'color' will now be grouped under a single
StyleInheritedData::copy() call instead of being spread out over
setFontDescription(), setLineHeight(), setColor(), etc.

Reviewed by Anders Carlsson.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@161184 268f45cc-cd09-0410-ab3c-d52691b4dbfc