Bug 887494 - Fix struct/class mismatch introduced by part 4 of 884124.  r=nnethercote.

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extra : rebase_source : 512f9f8c521c62c2efd4304dcca2205d82d7f8a5
Backout Bug 863398 for causing Bug 887519
Bug 885580 - Make sure that Compositor::GetBackend is only used [Cfrom the compositor thread. r=nical
Bug 705691 - Build cairo with the MUTEX option. r=mattwoodrow
Bug 887051 - Fix gamepad action key behavior in AwesomeScreen. r=kats