Prevent overflow of width/height of layout overflow rectangle which can cause scroll bar to misfunc…

Prevent overflow of width/height of layout overflow rectangle which can cause scroll bar to misfunction.

When a child element is positioned very far away the width/height of layout overflow rectangle may overflow. The patch detects such cases in RenderOverflow::addLayoutOverflow and shift the top/left edges of the rectangle to avoid overflow. 

BUG=267462
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=156567

[shuais_, 2013-08-21 08:07:49]

Please have a look. 

btw, the try bots are failing but I can't find out why, do you know where is the
log?

[eae, 2013-08-21 15:40:09]

We'd also like to see a layout test/regression test for all changes in behavior.

https://codereview.chromium.org/22799017/diff/1/Source/core/rendering/RenderO...
File Source/core/rendering/RenderOverflow.h (right):

https://codereview.chromium.org/22799017/diff/1/Source/core/rendering/RenderO...
Source/core/rendering/RenderOverflow.h:93: if (minX < 0 && maxX >= 0 && minX +
INT_MAX < maxX)
I don't understand what this code is trying to do. LayoutUnits are saturated so
they cannot overflow, instead the value is clamped to the LayoutUnit::min/max
range. Furthermore mixing integers and LayoutUnits like this is a bad idea as
they have very different ranges and precision.

[shuais_, 2013-08-22 08:36:48]

On 2013/08/21 15:40:09, eae wrote:
> We'd also like to see a layout test/regression test for all changes in
behavior.
> 
>
https://codereview.chromium.org/22799017/diff/1/Source/core/rendering/RenderO...
> File Source/core/rendering/RenderOverflow.h (right):
> 
>
https://codereview.chromium.org/22799017/diff/1/Source/core/rendering/RenderO...
> Source/core/rendering/RenderOverflow.h:93: if (minX < 0 && maxX >= 0 && minX +
> INT_MAX < maxX)
> I don't understand what this code is trying to do. LayoutUnits are saturated
so
> they cannot overflow, instead the value is clamped to the LayoutUnit::min/max
> range. Furthermore mixing integers and LayoutUnits like this is a bad idea as
> they have very different ranges and precision.

Improved the patch to not mix them. I might have been confusing by saying the
width/height overflow, but the width/height of the merged rectangle might be
twice as LayoutUnit can represent, in which case the old behavior is to not
change x,y and clamp width/height, the wrong result would be propagated to body
ultimately and cause it to think no scroll bar is needed. With my patch the new
behavior is to fix the bottom/right edge of the merged rectangle and move x,y if
needed, because the bottom right point is what matters in calculating scrolling
area.

[eae, 2013-08-22 16:01:37]

LGTM

[commit-bot: I haz the power, 2013-08-22 16:01:57]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/shuais@opera.com/22799017/16001

[commit-bot: I haz the power, 2013-08-22 17:39:50]

Change committed as 156567