Fix segfault caused by document wrapper being GCed.

[jdm]

No description provided.

[metajack]

r+

[bors-servo]

saw approval from metajack
at jdm@9640324

[bors-servo]

merging jdm/servo/sandbox = 9640324 into auto

[bors-servo]

jdm/servo/sandbox = 9640324 merged ok, testing candidate = 39252b2

[bors-servo]

all tests pass:
http://servo-buildbot.pub.build.mozilla.org/builders/linux/builds/352
http://servo-buildbot.pub.build.mozilla.org/builders/mac/builds/307

[bors-servo]

fast-forwarding master to auto = 39252b2

[DavidBruant]

One of the most important game changer for web developers. This almost makes effectively WebWorkers useless.
Canvas rendering can now be done in parallel without resort to new (arguably awkward) API (just open a sandboxed iframe and render there)

<3 that is all. Thanks @jdm and @bors-servo !

[jdm]

This requires servo/rust-mozjs#36.

[metajack]

r+

[bors-servo]

saw approval from metajack
at jdm@636c30a

[bors-servo]

merging jdm/servo/gccrash = 636c30a into auto

[bors-servo]

jdm/servo/gccrash = 636c30a merged ok, testing candidate = 2372a84

[bors-servo]

all tests pass:
http://servo-buildbot.pub.build.mozilla.org/builders/linux/builds/353
http://servo-buildbot.pub.build.mozilla.org/builders/mac/builds/308

[bors-servo]

fast-forwarding master to auto = 2372a84

[DavidBruant]

You may want to take a look at this bug and its patch
Should I open an issue?

[jdm]

Yes please!

[DavidBruant]

Sort of made an umbrella issue servo#934