gfx: Update rust-azure to pick up arcs, gradients, and subpixel text
Update toml.py to upstream 1069d2449760525535ca77514a92e9237ee0deaf
gfx: Switch the default to CPU painting.

We've discussed this some and I think there's consensus to do it as a
pragmatic decision for now. CPU painting is more stable, especially with
buggy drivers, and faster (because we aren't caching the necessary
OpenGL objects yet and possibly for other reasons), so it provides a
better "out of the box" experience for newcomers to Servo who don't know
to pass the `-c` option. This patch continues to reftest both Skia and
Skia-GL out of a desire to keep options open. Skia-GL remains a
first-class citizen.
properly incrementally set block size
Remove the help text for render backend option. follow up #3711.
Use DOMRefCell for Document.
Use DOMRefCell for Event.
Use DOMRefCell for EventTarget.
Use DOMRefCell for FormData.
Use DOMRefCell for HTMLImageElement.
Use DOMRefCell for HTMLInputElement.
Use DOMRefCell for Node.

Altough LayoutDataRef is touched, we don't use DOMRefCell in it becasuse
it's expected to manipulate in other task.
Use DOMRefCell for Window.
Use DOMRefCell for ServoHTMLParser.
Use DOMRefCell for URLSearchParams.
Use DOMRefCell for XMLHttpRequest.
Use DOMRefCell for TimerManager.
Use DOMRefCell for ScriptTask.
Use DOMRefCell for Page.
auto merge of #3749 : pcwalton/servo/update-rust-azure, r=metajack

r? @metajack