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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- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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components/script_traits/lib.rs

@@ -69,7 +69,7 @@ use std::sync::mpsc::{Receiver, Sender, RecvTimeoutError};
 use style_traits::CSSPixel;
 use style_traits::SpeculativePainter;
 use webdriver_msg::{LoadStatus, WebDriverScriptCommand};
-use webrender_api::{ClipId, DevicePixel, ImageKey};
+use webrender_api::{ClipId, DevicePixel, DocumentId, ImageKey};
 use webvr_traits::{WebVREvent, WebVRMsg};
 
 pub use script_msg::{LayoutMsg, ScriptMsg, EventResult, LogEntry};
@@ -554,7 +554,9 @@ pub struct InitialScriptState {
     /// A channel to the webgl thread used in this pipeline.
     pub webgl_chan: WebGLPipeline,
     /// A channel to the webvr thread, if available.
-    pub webvr_chan: Option<IpcSender<WebVRMsg>>
+    pub webvr_chan: Option<IpcSender<WebVRMsg>>,
+    /// The Webrender document ID associated with this thread.
+    pub webrender_document: DocumentId,
 }
 
 /// This trait allows creating a `ScriptThread` without depending on the `script`