Fix offscreen canvas transfer with closure (#11427)

AUTHORS

@@ -478,4 +478,5 @@ a license to everyone to use it as detailed in LICENSE.)
 * Robert Aboukhalil <robert.aboukhalil@gmail.com>
 * Jonathan Poelen <jonathan.poelen@gmail.com>
 * Ashley Hauck <github@khyperia.com>
+* Junyue Cao <junyuecao@gmail.com>
 * Elías Serrano <feserr3@gmail.com>

src/library_pthread.js

@@ -531,12 +531,13 @@ var LibraryPThread = {
         'selfThreadId': threadParams.pthread_ptr, // TODO: Remove this since thread ID is now the same as the thread address.
         'parentThreadId': threadParams.parent_pthread_ptr,
         'stackBase': threadParams.stackBase,
-        'stackSize': threadParams.stackSize,
+        'stackSize': threadParams.stackSize
+    };
 #if OFFSCREENCANVAS_SUPPORT
-        'moduleCanvasId': threadParams.moduleCanvasId,
+    // Note that we do not need to quote these names because they are only used in this file, and not from the external worker.js.
-        'offscreenCanvases': threadParams.offscreenCanvases,
+    msg.moduleCanvasId = threadParams.moduleCanvasId;
+    msg.offscreenCanvases = threadParams.offscreenCanvases;
 #endif
-      };
     worker.runPthread = function() {
       // Ask the worker to start executing its pthread entry point function.
       msg.time = performance.now();