Auto merge of #18592 - MortimerGoro:dom_texture, r=jdm

Implement DOM to texture

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This is a prototype of the WebGL DOMToTexture feature. The API should be fine as a privileged extension for now due to security concerns. The working group has been investigating the viability of unprivileged usage but the spec is not ready yet.

Demo video: https://www.youtube.com/watch?v=hpZqEM5hPao

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- [ ] These changes fix #__ (github issue number if applicable).

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components/constellation/pipeline.rs

@@ -511,6 +511,7 @@ impl UnprivilegedPipelineContent {
             content_process_shutdown_chan: self.script_content_process_shutdown_chan,
             webgl_chan: self.webgl_chan,
             webvr_chan: self.webvr_chan,
+            webrender_document: self.webrender_document,
         }, self.load_data.clone());
 
         LTF::create(self.id,