Add broken demo to investigate

addons/xterm-addon-canvas/src/CanvasAddon.ts

@@ -25,9 +25,7 @@ export class CanvasAddon extends Disposable implements ITerminalAddon {
   public activate(terminal: Terminal): void {
     const core = (terminal as any)._core;
     if (!terminal.element) {
-      this.register(toDisposable(() => {
-        core.onWillOpen(() => this.activate(terminal));
-      }));
+      this.register(core.onWillOpen(() => this.activate(terminal)));
       return;
     }
 

addons/xterm-addon-webgl/src/WebglAddon.ts

@@ -33,9 +33,7 @@ export class WebglAddon extends Disposable implements ITerminalAddon {
     }
     const core = (terminal as any)._core;
     if (!terminal.element) {
-      this.register(toDisposable(() => {
-        core.onWillOpen(() => this.activate(terminal));
-      }));
+      this.register(core.onWillOpen(() => this.activate(terminal)));
       return;
     }
     this._terminal = terminal;

addons/xterm-addon-webgl/src/WebglRenderer.ts

@@ -103,6 +103,9 @@ export class WebglRenderer extends Disposable implements IRenderer {
       throw new Error('WebGL2 not supported ' + this._gl);
     }
 
+    // TODO: Remove me.
+    throw new Error('WebGL2 not supported ' + this._gl);
+
     this.register(addDisposableDomListener(this._canvas, 'webglcontextlost', (e) => {
       console.log('webglcontextlost event received');
       // Prevent the default behavior in order to enable WebGL context restoration.