[New Multicolumn] Support for paged overflow.

[New Multicolumn] Support for paged overflow.

This brings support for overflow-y:-webkit-paged-[xy] to the new
multicol implementation.

BUG=359976

[rune, 2014-06-18 22:09:05]

I have the same comment about tests as in:

https://codereview.chromium.org/299373006/#msg2

https://codereview.chromium.org/295373006/diff/1/Source/core/rendering/Render...
File Source/core/rendering/RenderBlockFlow.cpp (right):

https://codereview.chromium.org/295373006/diff/1/Source/core/rendering/Render...
Source/core/rendering/RenderBlockFlow.cpp:2785: return style->isOverflowPaged()
&& renderer->node() != renderer->document().viewportDefiningElement();
"this" is always passed as renderer. Why not make this a class method?

https://codereview.chromium.org/295373006/diff/1/Source/core/rendering/Render...
Source/core/rendering/RenderBlockFlow.cpp:2799: 
We can get rid of this code duplication. Also we can have an enumerated type
instead of two booleans.

How about (modulo naming):

FlowThreadType { None, MultiColumn, Paged }

FlowThreadType flowThreadType(const RenderStyle* style) {
    if (isPagedOverflow(style))
        return Paged;
    if (style->specifiesColumns())
        return MultiColumn;
    return None;
}

and then  compare new/old FlowThreadType.

https://codereview.chromium.org/295373006/diff/1/Source/core/rendering/Render...
File Source/core/rendering/RenderMultiColumnSet.cpp (right):

https://codereview.chromium.org/295373006/diff/1/Source/core/rendering/Render...
Source/core/rendering/RenderMultiColumnSet.cpp:607: blockOffset = i * colGap;

I had to stare at this for a while. I think this warrants a comment, or perhaps
rename colGap to pageSpacing or something. If you're not mstensho, this I
believe is due to the fact that the column-gap property is misused to apply
spacing between pages for overflow:paged-x/y. Not only when fragments are
"stacked" in the inline direction, but also in the block direction. For block
direction stacking, the coordinates follow the flow-thread coordinates, but we
have to add the colGap spacing that is added after each of the 'i' pages.

[rune, 2014-06-19 09:22:19]

https://codereview.chromium.org/295373006/diff/1/Source/core/rendering/Render...
File Source/core/rendering/RenderMultiColumnSet.cpp (right):

https://codereview.chromium.org/295373006/diff/1/Source/core/rendering/Render...
Source/core/rendering/RenderMultiColumnSet.cpp:607: blockOffset = i * colGap;
On 2014/06/18 22:09:05, rune wrote:
> 
> I had to stare at this for a while. I think this warrants a comment, or
perhaps
> rename colGap to pageSpacing or something.

Never mind renaming. This is in RenderMultiColumnSet and even if the block
direction stacking is only used for paged overflow, it doesn't make sense to use
pageSpacing. Still would like a comment about column-gap applying as "vertical"
spacing between fragments stacked in the block direction.

[rune, 2014-07-08 11:15:36]

This CL may be closed now as this replacement CL has landed: 

https://codereview.chromium.org/364233005/

[Julien - ping for review, 2014-07-08 15:12:04]

On 2014/07/08 11:15:36, rune (futhark.irc - CET) wrote:
> This CL may be closed now as this replacement CL has landed: 
> 
> https://codereview.chromium.org/364233005/

Thanks rune, closed.