Subpixel rendering: Zero sized compositing container's content positioned off by one device pixel.
https://bugs.webkit.org/show_bug.cgi?id=134903

Reviewed by Simon Fraser.

The compositing layer boundaries are calculated using its renderer()'s and the renderer()'s
descendants' bounds. However when the renderer() is zero sized, its bounds are omitted.
In such cases, when the child content has offset from the renderer(), the subpixel adjustment
of the compositing layer becomes negative (-meaning that the compositing layer is to the right/bottom
direction from its renderer()). Remove fabs() to be able to express such direction.

Source/WebCore:
Test: compositing/hidpi-compositing-layer-with-zero-sized-container.html

* rendering/RenderLayerBacking.cpp:
(WebCore::RenderLayerBacking::updateGeometry):

LayoutTests:
* compositing/hidpi-compositing-layer-with-zero-sized-container-expected.html: Added.
* compositing/hidpi-compositing-layer-with-zero-sized-container.html: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@171100 268f45cc-cd09-0410-ab3c-d52691b4dbfc
[iOS] Don't progressively re-render tiles while pinch-zooming under memory pressure.
<https://webkit.org/b/134915>

When we're under memory pressure, the last thing we want to be doing is
creating gratuitous new IOSurfaces. Just wait for the gesture to end before
rendering at the new scale.

Reviewed by Tim Horton.

* WebProcess/WebPage/ios/WebPageIOS.mm:
(WebKit::WebPage::updateVisibleContentRects):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@171101 268f45cc-cd09-0410-ab3c-d52691b4dbfc