Add throwOnFail to groupCall.setScreensharingEnabled (#2787)

* Add throwOnFail to groupCall.setScreensharingEnabled

For https://github.com/vector-im/element-call/pull/652

* Update mediaHandler.ts

src/webrtc/groupCall.ts

@@ -600,6 +600,7 @@ export class GroupCall extends TypedEventEmitter<
 
                 return true;
             } catch (error) {
+                if (opts.throwOnFail) throw error;
                 logger.error("Enabling screensharing error", error);
                 this.emit(GroupCallEvent.Error,
                     new GroupCallError(GroupCallErrorCode.NoUserMedia, "Failed to get screen-sharing stream: ", error),

src/webrtc/mediaHandler.ts

@@ -33,6 +33,11 @@ export type MediaHandlerEventHandlerMap = {
 export interface IScreensharingOpts {
     desktopCapturerSourceId?: string;
     audio?: boolean;
+    // For electron screen capture, there are very few options for detecting electron
+    // apart from inspecting the user agent or just trying getDisplayMedia() and
+    // catching the failure, so we do the latter - this flag tells the function to just
+    // throw an error so we can catch it in this case, rather than logging and emitting.
+    throwOnFail?: boolean;
 }
 
 export class MediaHandler extends TypedEventEmitter<