The goal of this work is to remove all references to the ipc-channel crate from WebRender and move all IPC usage into the calling code in Servo instead. This will require a few parts:

• replace all uses of IPC channels in WebRender with std::mpsc channels instead
• use the modified version of WebRender in Servo
• create an IPC channel that is stored in Constellation which is used for cross-process communication with WebRender
• create a new type like webrender_api::RenderApiSender that uses an IPC channel to pass the messages to the parent
• make the IPC channel route the messages to the in-process webrender_api::RenderApiSender

Code: components/layout_thread/lib.rs, components/layout_traits/lib.rs, components/constellation/constellation.rs, components/constellation/pipeline.rs

To consider the task complete, it should be enough to demonstrate that ./mach run tests/html/about-blank.html still renders a page after the changes are made.