[CSS Blending] The composited layers isolated by the page group should blend with the default white background color.
https://bugs.webkit.org/show_bug.cgi?id=136563

Reviewed by Simon Fraser.

Source/WebCore:

If a blending layer is not isolated, then it should blend with a white backdrop:
http://dev.w3.org/fxtf/compositing-1/#pagebackdrop

Tests: css3/blending/blend-mode-body-composited-child-background-color.html
       css3/blending/blend-mode-body-composited-child.html

* rendering/RenderLayerBacking.cpp:
(WebCore::RenderLayerBacking::isSimpleContainerCompositingLayer):
If the isolating composited layer is the root renderer, then it should have a backing store
into which the initial white backdrop will be painted.

LayoutTests:

* css3/blending/blend-mode-blended-element-overlapping-composited-sibling-should-have-compositing-layer-expected.txt:
* css3/blending/blend-mode-body-composited-child-background-color-expected.html: Added.
* css3/blending/blend-mode-body-composited-child-background-color.html: Added.
* css3/blending/blend-mode-body-composited-child-expected.html: Added.
* css3/blending/blend-mode-body-composited-child.html: Added.
* css3/blending/blend-mode-parent-of-composited-blended-has-layer-expected.txt:
* css3/blending/blend-mode-with-composited-descendant-should-have-layer-expected.txt:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@173867 268f45cc-cd09-0410-ab3c-d52691b4dbfc
[CSS Grid Layout] Do not grow tracks when the growth factor is 0
https://bugs.webkit.org/show_bug.cgi?id=136575

Reviewed by Darin Adler.

A couple of performance optimizations for the track sizing
algorithm. On the one hand we avoid the computation of the
available logical space share if the track has no growth potential
(the current breadth is the maximum breadth) and on the other
hand, we avoid calling RenderGrid::distributeSpaceToTracks() if
the available logical space is not greater than 0.

The combined effect of these two changes is an impressive +16%
improvement in auto-grid-lots-of-data.html performance test.

No new tests as there is no change in the functionality.

* rendering/RenderGrid.cpp:
(WebCore::RenderGrid::resolveContentBasedTrackSizingFunctionsForItems):
(WebCore::RenderGrid::distributeSpaceToTracks):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@173868 268f45cc-cd09-0410-ab3c-d52691b4dbfc