Use last resort font when only there is no font in font group.
There is a little bit of performance gain of layout.
removing unnecessary to_owned
Merge pull request #1341 from deokjinkim/layout_font_optimize

Use last resort font when only there is no font in font group.
Merge pull request #1343 from ryanhc/removing_to_owned

removing unnecessary to_owned
Remove unnecessary @mut from LineboxScanner
Convert LayoutContext.image_cache from @mut to MutexArc

LocalImageCache isn't Freeze so we have to use unsafe_access,
which exists for MutexArc and not RWArc.
Merge pull request #1344 from kmcallister/layout-boxes

Remove @mut from LineboxScanner and image caching
remove @ from FontContextHandle in linux
remove SendableTextRun & remove @mut Font From TextRun&Shaper(Font),Font.shaper,
       fontfamily,fontgroup,render_context.font_ctx
remove @ fontcontext
Patch for macos
fix indent & some code
Merge pull request #1342 from ksh8281/remove_@_from_font_context

Remove @ from font context, remove SendableTextRun
remove @ from net/image_cache_task

~[Chan<ImageResponseMsg>] is not freezetype.
so we have to use unsafe_access
Remove orphaned gfx::text::shaper code

The shaper code referenced in this issue is no longer being used.  It
was removed in commit a535f221469940d9549550953b845010a353d3bc, but
later reintroduced due to a merge conflict in commit
d64d987e1da66691ccd0e7e04fd54babc2c5bab4.

Fixes #163.
Merge pull request #1347 from ksh8281/remove_@_from_net_image_cache_task

remove @ from net/image_cache_task
Merge pull request #1348 from dhedlund/issue_163

Remove orphaned gfx::text::shaper code
add namespaces to elements
auto merge of #1358 : therealglazou/servo/therealglazou/namespaces, r=jdm

Add a namespace to elements. Sets by default the namespace to HTML for elements created by hubbub. Fixes :nth-of-type() and friends to match the namespace.

Note: prefix is not added by this PR because hubbub does not preserve it and I wanted to keep the patch as simple as possible.
Change Namespace::to_str() to not allocate and return a reference.