Building C++ to target Javascript (e.g., asm.js) and execute C++ in the browser is becoming quite the popular indoor sport. Here's a current presentation and experience report:

C++ on the Web: Run your big 3D Game in the browser! (slides) by Andre Weissflog

Head of Development, Berlin

Bigpoint GmbH My presentation about porting large C/C++ code bases to the browser (emscripten, flascc, Google Native Client)

From the Wrap-up slide: