Include WebViewId into EmbedderMsg variants where possible (#35211)

`EmbedderMsg` was previously paired with an implicit
`Option<WebViewId>`, even though almost all variants were either always
`Some` or always `None`, depending on whether there was a `WebView
involved.

This patch adds the `WebViewId` to as many `EmbedderMsg` variants as
possible, so we can call their associated `WebView` delegate methods
without needing to check and unwrap the `Option`. In many cases, this
required more changes to plumb through the `WebViewId`.

Notably, all `Request`s now explicitly need a `WebView` or not, in order
to ensure that it is passed when appropriate.

Signed-off-by: Delan Azabani <dazabani@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>

components/script/dom/globalscope.rs

@@ -16,7 +16,7 @@ use std::{mem, ptr};
 
 use base::id::{
     BlobId, BroadcastChannelRouterId, MessagePortId, MessagePortRouterId, PipelineId,
-    ServiceWorkerId, ServiceWorkerRegistrationId,
+    ServiceWorkerId, ServiceWorkerRegistrationId, WebViewId,
 };
 use content_security_policy::{CheckResult, CspList, PolicyDisposition};
 use crossbeam_channel::Sender;
@@ -691,6 +691,20 @@ impl FileListener {
 }
 
 impl GlobalScope {
+    /// A sender to the event loop of this global scope. This either sends to the Worker event loop
+    /// or the ScriptThread event loop in the case of a `Window`. This can be `None` for dedicated
+    /// workers that are not currently handling a message.
+    pub(crate) fn webview_id(&self) -> Option<WebViewId> {
+        if let Some(window) = self.downcast::<Window>() {
+            Some(window.webview_id())
+        } else if let Some(dedicated) = self.downcast::<DedicatedWorkerGlobalScope>() {
+            dedicated.webview_id()
+        } else {
+            // ServiceWorkerGlobalScope, PaintWorklet, or DissimilarOriginWindow
+            None
+        }
+    }
+
     #[allow(clippy::too_many_arguments)]
     pub(crate) fn new_inherited(
         pipeline_id: PipelineId,