Remove the hardcoded alert message on WebGL context loss event in library_browser.js, since it prevents applications from benignly handling WebGL context loss events by reloading GL assets from disk.
Add new function emscripten_is_webgl_context_lost() that allows code to directly query to confirm the WebGL context loss status.
Move the default WebGL context lost message to the default shell.html file so that default applications still show the error message, and applications can easily override the behavior if/when they see fit.
Merge pull request #2348 from juj/context_lost

WebGL context loss handling improvements.