Add FINAL decorators to the InlineBox class hierarchy.
<http://webkit.org/b/115177>

Reviewed by Antti Koivisto.

From Blink r148628 by <cevans@chromium.org>:

FINAL is a macro in wtf/Compiler.h that does the correct thing if the compiler does not support "final")
The approach used is as simple as possible whilst being thorough.
So, leaf classes have FINAL applied to the whole class whereas intermediary classes have FINAL applied to relevant methods.

FINAL allows a compiler to devirtualize call sites and turn them into direct calls. As you might expect, this is perf positive:
(clang on Linux):
- line_layout.html goes from 120 runs/s -> 123 runs/2, +2.5%
- html5-full-render.html goes from 3176ms -> 3162ms, +0.4%

I have confidence that the former result is statistically significant (as the numbers are very very stable) but not the latter.

* rendering/EllipsisBox.h:
* rendering/InlineFlowBox.h:
* rendering/InlineTextBox.h:
* rendering/RootInlineBox.h:
* rendering/TrailingFloatsRootInlineBox.h:
* rendering/svg/SVGInlineFlowBox.h:
* rendering/svg/SVGInlineTextBox.h:
* rendering/svg/SVGRootInlineBox.h:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149110 268f45cc-cd09-0410-ab3c-d52691b4dbfc