Commits on May 20, 2016

1. Expand viewports to consist of a rectangle and a transform. …

   Further work should expand this to an entire rectangle/transform stack,
   but this is an improvement over the current situation.
   
   This was necessary to properly handle clipping in the presence of
   nested iframes and `overflow: scroll` stacking contexts, while
   simultaneously handling transformed and clipped iframes.
   
   We still have some clipping issues when `overflow: scroll`, iframes, and
   transforms are all nested together: this is visible in the browser.html
   tab change animation on duckduckgo.com result pages. I wanted to get
   this in now, though, because this significantly improves the current
   situation.
   
   Addresses servo/servo#11150.
   Addresses servo/servo#11151.

   

   pcwalton committed May 20, 2016

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