Add basic support for web fonts. Synchronous loading only
for now, and only deals with TTF format fonts.

For an example, try loading http://icons.marekventur.de
Fix missing license header in new file.
Address review comments.
Don't rely on font hint for format detection. Handle parsing comma
separated format hints. Fix oversight in mac code dealing with
creating web fonts from memory.
Update font face to new url parser.
Add pointers to the relevant issue for some bugs.
Assert that we're handed a DOM global in initialize_global.
Move CanvasRenderTask to gfx crate.
Merge pull request #2932 from Ms2ger/fixme-347

Add pointers to the relevant issue for some bugs; r=jdm
Track rerender msgs

If the compositor outputs to a file:
* Track rerender msgs sent from the compositor to the render tasks.
* Before outputting, wait until all rerender msgs are processed by the
  render tasks.

Fixes issue https://github.com/servo/servo/issues/2871.
Merge pull request #2930 from bjwbell/track-rerender-msgs

Track rerender msgs
Implement Location.hash.
Merge pull request #2935 from Ms2ger/location-hash

Implement Location.hash.
Merge pull request #2933 from Ms2ger/initialize_global

Assert that we're handed a DOM global in initialize_global.
Pass a non-nullable string to NamedGetter.

There is no actual reason to use a nullable string here; all callers have a
string they want to pass.

The issue dates back to the time that DOMString was inherently nullable
(before #1215); this API was not converted back to the non-nullable DOMString
type after that landed.
Remove an unused argument to needCx and use it in CGCallGenerator.
Introduce a PerformanceTimingHelpers trait for the NavigationStartPrecise method.
Remove references to nullable any from testbinding.

'any' is inherently nullable, so nullable any doesn't exist.
Comment out references to floating-point arguments with default values.

Our parser does not support floating-point constants, so we can't use default
values for floating-point types.
Add methods that return floating-point types to TestBinding.webidl.

They were already implemented in testbinding.rs, but were forgotten in the IDL
file.