Bug 1675764 [Wayland] Don't use screen sharing preview with PipeWire, r=jib

When screen sharing preview is generated a system dialog is fired and the same system dialog
is fired again when an actual sharing is performed.

Shared resource is selected by system dialog only, we don't have any control which system resource
will be shared over PipeWire. So there's no point to generate a preview of a resource which may not be shared
as an user can select a different resorce.

The preview should be generated by system dialog where the shared resource is selected and confirmed,
we only consume that user selection.

Depends on D96694

Differential Revision: https://phabricator.services.mozilla.com/D96806

browser/actors/WebRTCParent.jsm

@@ -761,6 +761,8 @@ function prompt(aActor, aBrowser, aRequest) {
         );
         menupopup.appendChild(doc.createXULElement("menuseparator"));
 
+        let isPipeWire = false;
+
         // Build the list of 'devices'.
         let monitorIndex = 1;
         for (let i = 0; i < devices.length; ++i) {
@@ -788,6 +790,7 @@ function prompt(aActor, aBrowser, aRequest) {
             // Don't mark it as scary as there's an extra confirmation step by
             // PipeWire portal dialog.
             if (name == PIPEWIRE_PORTAL_NAME && device.id == PIPEWIRE_ID) {
+              isPipeWire = true;
               let sawcStringId = "getUserMedia.sharePipeWirePortal.label";
               let item = addDeviceToList(
                 menupopup,
@@ -913,39 +916,41 @@ function prompt(aActor, aBrowser, aRequest) {
             perms.EXPIRE_SESSION
           );
 
-          video.deviceId = deviceId;
-          let constraints = {
-            video: { mediaSource: type, deviceId: { exact: deviceId } },
-          };
-          chromeWin.navigator.mediaDevices.getUserMedia(constraints).then(
-            stream => {
-              if (video.deviceId != deviceId) {
-                // The user has selected a different device or closed the panel
-                // before getUserMedia finished.
-                stream.getTracks().forEach(t => t.stop());
-                return;
+          if (!isPipeWire) {
+            video.deviceId = deviceId;
+            let constraints = {
+              video: { mediaSource: type, deviceId: { exact: deviceId } },
+            };
+            chromeWin.navigator.mediaDevices.getUserMedia(constraints).then(
+              stream => {
+                if (video.deviceId != deviceId) {
+                  // The user has selected a different device or closed the panel
+                  // before getUserMedia finished.
+                  stream.getTracks().forEach(t => t.stop());
+                  return;
+                }
+                video.srcObject = stream;
+                video.stream = stream;
+                doc.getElementById("webRTC-preview").hidden = false;
+                video.onloadedmetadata = function(e) {
+                  video.play();
+                };
+              },
+              err => {
+                if (
+                  err.name == "OverconstrainedError" &&
+                  err.constraint == "deviceId"
+                ) {
+                  // Window has disappeared since enumeration, which can happen.
+                  // No preview for you.
+                  return;
+                }
+                Cu.reportError(
+                  `error in preview: ${err.message} ${err.constraint}`
+                );
               }
-              video.srcObject = stream;
-              video.stream = stream;
-              doc.getElementById("webRTC-preview").hidden = false;
-              video.onloadedmetadata = function(e) {
-                video.play();
-              };
-            },
-            err => {
-              if (
-                err.name == "OverconstrainedError" &&
-                err.constraint == "deviceId"
-              ) {
-                // Window has disappeared since enumeration, which can happen.
-                // No preview for you.
-                return;
-              }
-              Cu.reportError(
-                `error in preview: ${err.message} ${err.constraint}`
-              );
-            }
-          );
+            );
+          }
         };
         menupopup.addEventListener("command", menupopup._commandEventListener);
       }