Merge 122861 - Incorrect offset used for scrollWidth/Height calculation

Merge 122861 - Incorrect offset used for scrollWidth/Height calculation
https://bugs.webkit.org/show_bug.cgi?id=91461

Reviewed by Eric Seidel.

Source/WebCore:

Due to a different offset being used to calculate the scrollWidth/Height
and pixelSnappedClientWidth/Height the scroll value can be off by one in
same cases. This can causes scrollbars to appear even when there is no
overflow.

Test: fast/sub-pixel/block-with-margin-overflow.html

* rendering/RenderBox.cpp:
(WebCore::RenderBox::scrollWidth):
Change location offset passed to snapSizeToPixel to include x() to match
offset used by pixelSnappedClientWidth.

(WebCore::RenderBox::scrollHeight):
Change location offset passed to snapSizeToPixel to include y() to match
offset used by pixelSnappedClientHeight.

* rendering/RenderLayer.cpp:
(WebCore::RenderLayer::clampScrollOffset):
Change calculation to use pixelSnappedClientWidth/Height as it is
subtracted from the pixel snapped scrollWidth/Height values.

(WebCore::RenderLayer::scrollWidth):
(WebCore::RenderLayer::scrollHeight):
Change RenderLayer versions of scrollWidth/Height to include x()/y() as
per the RenderBox versions.

LayoutTests:

Add new test ensuring that a block that shouldn't have overflow doesn't
have scrollbars.

* fast/sub-pixel/block-with-margin-overflow-expected.html: Added.
* fast/sub-pixel/block-with-margin-overflow.html: Added.
* platform/chromium-win/fast/block/float/026-expected.txt:
* platform/chromium-win/fast/block/float/028-expected.txt:
* platform/chromium-win/fast/block/float/overhanging-tall-block-expected.txt:
* platform/mac/fast/multicol/shrink-to-column-height-for-pagination-expected.png:
* platform/mac/fast/multicol/shrink-to-column-height-for-pagination-expected.txt:
Update test expectations that incorrectly had overflow.


TBR=eae@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=123234