Send in the right container block size for relative positioning.

This fixes #1757.
Remove Node.hasAttributes() method that was removed from the specification.
auto merge of #1835 : Ms2ger/servo/hasAttributes, r=metajack
Add some tests for string codegen.
Add tests for optional nullable arguments without default values.
Add interface codegen tests.
auto merge of #1839 : Ms2ger/servo/optional-test, r=jdm
Add disabled tests for optional nullable arguments with non-null default values.
Inline dataLoc in the one place that can see it and the one place that can't.
Avoid a type error with a non-null default value for an optional nullable primitive argument.
Avoid a type error with a non-null default value for an optional nullable string argument.
auto merge of #1846 : Ms2ger/servo/non-null-default, r=jdm
Common up some code in the conversion to nullable and non-nullable primitive types.
Simplify the code flow in the conversion to primitive types so that default values are handled together.
Common up some more code in the handling of default values for primitive types.
Removed glob imports from CodegenRust.py

Removed glob imports from CodegenRust.py (code review changes)

Removed many glob imports from CodegenRust.py (code review changes)

Removed glob imports from CodegenRust.py (cleanup)
auto merge of #1787 : hgentry/servo/mozilla-servo, r=jdm

Fixes #1779. Most of them were able to be replaced without issue.
implement the setter for Node.nodeValue.(fixes #1825)
Don't initialize nullable interface arguments to None in codegen.

This allows Rust to check that we've actually initialized all cases.
Pass Option<JSVal> for optional JSVals.