Refactor RenderStyle::diff to be grouped by type and guard with pointer compares on structs

Refactor RenderStyle::diff to be grouped by type and guard with pointer compares on structs

This patch moves around the checks inside RenderStyle::diff so that as
much a possible the checks for a given structure of data are all grouped
and then guards those checks with a pointer compare on the struct when
possible. This was already done for some of the structs but not all of
them.

I also noticed that the logic for table display types had not been updated
for flex box so I removed the >= TABLE check and replaced it with a
LAST_TABLE_DISPLAY and FIRST_TABLE_DISPLAY guard cutting out a bunch of
if checks for flex boxes.

Similarly we were deep comparing the SVGRenderStyle because we were using
the overloaded operator== on the DataRef<SVGRenderStyle> before calling
into ::diff() to do the real comparison which is a waste. I changed to a
pointer comparison which will reduce the number of duplicate checks for
SVG elements.

While this is definitely a set of micro-optimizations it should reduce
the number of checks for a typical RenderStyle::diff which is very hot
code in all our benchmarks.

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=165037

[ojan, 2014-01-14 00:49:35]

lgtm

https://codereview.chromium.org/136693009/diff/1/Source/core/rendering/style/...
File Source/core/rendering/style/RenderStyle.cpp (right):

https://codereview.chromium.org/136693009/diff/1/Source/core/rendering/style/...
Source/core/rendering/style/RenderStyle.cpp:373: if (m_svgStyle.get() !=
other->m_svgStyle.get()) {
If you're going to add all these ".get()" calls, I think it deserves an
expalantory comment why.

[esprehn, 2014-01-14 04:20:14]

On 2014/01/14 00:49:35, ojan wrote:
> lgtm
> 
>
https://codereview.chromium.org/136693009/diff/1/Source/core/rendering/style/...
> File Source/core/rendering/style/RenderStyle.cpp (right):
> 
>
https://codereview.chromium.org/136693009/diff/1/Source/core/rendering/style/...
> Source/core/rendering/style/RenderStyle.cpp:373: if (m_svgStyle.get() !=
> other->m_svgStyle.get()) {
> If you're going to add all these ".get()" calls, I think it deserves an
> expalantory comment why.

Done.

[commit-bot: I haz the power, 2014-01-14 04:29:40]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/esprehn@chromium.org/136693009/60001

[commit-bot: I haz the power, 2014-01-14 07:59:19]

Change committed as 165037