title: Is generateMipmap done?
body: <p>In my app I generate mipmaps for the 6x4096x4096 cube map texture. Next I need to undertake some other changes on that texture that are time dependent. All the drawing is done inside of the requestAnimationFrame's loop. </p>
  
  <p>Depending on the browser, device, etc., sometimes it takes three, sometimes four or even five consecutive frames of the loop to finally generate those mipmaps, and I need to know in which frame exactly mipmaps are already done.</p>
  
  <p>So the question is: how to check in which frame of the requestAnimationFrame's loop mipmaps generated for the "TEXTURE_CUBE_MAP" by the WebGL's command "generateMipmap" are ready? Is there some flag for checking status of the "generateMipmap" completion?</p>