We want to be able to send IPC messages from the translation in the parent. So
the simplest thing it move the top level actor parts of CanvasParent into
CanvasTranslator.
This patch also moves the canvas thread management parts out into a new
CanvasThreadHolder class and hopefully makes the lifecycle management of these
much more robust. This includes the use of a TaskQueue per CanvasTranslator to
manage serial processing on the canvas workers, instead of a boolean.
Differential Revision: https://phabricator.services.mozilla.com/D60887
--HG--
rename : gfx/layers/ipc/CanvasParent.cpp => gfx/layers/ipc/CanvasThread.cpp
rename : gfx/layers/ipc/CanvasParent.h => gfx/layers/ipc/CanvasThread.h
rename : gfx/layers/CanvasTranslator.cpp => gfx/layers/ipc/CanvasTranslator.cpp
rename : gfx/layers/CanvasTranslator.h => gfx/layers/ipc/CanvasTranslator.h
extra : moz-landing-system : lando