webassembly: Support piping in a program on stdin.

The performance benchmark suite can now be run on the webassembly port.

Signed-off-by: Damien George <damien@micropython.org>

ports/webassembly/wrapper.js

@@ -56,6 +56,12 @@ var mainProgram = function()
               repl = false;;
           }
       }
+
+      if (process.stdin.isTTY === false) {
+          contents = fs.readFileSync(0, 'utf8');
+          repl = 0;
+      }
+
       mp_js_init(heap_size);
 
       if (repl) {