I was wondering if WebGL is considered stable enough to be enabled by default. It makes some PDFs render much faster and it has been off by default for a while now, so we have had quite some time to test it.

If we decide to enable WebGL by default, we should not forget to update https://github.com/mozilla/pdf.js/blob/master/extensions/chromium/preferences_schema.json#L39 as well.

/cc @yurydelendik 
/cc @Snuffleupagus (because IIRC you were testing WebGL too)

gl.clearColor(0, 0, 0, 0);
    }
    gl.clear(gl.COLOR_BUFFER_BIT);
    const coordsBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, coordsBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, coords, gl.STATIC_DRAW);
    gl.enableVertexAttribArray(cache.positionLocation);
    gl.vertexAttribPointer(cache.positionLocation, 2, gl.FLOAT, false, 0, 0);
    const colorsBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, colorsBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, colors, gl.STATIC_DRAW);
    gl.enableVertexAttribArray(cache.colorLocation);
    gl.vertexAttribPointer(
      cache.colorLocation,
      3,
      gl.UNSIGNED_BYTE,
      false,
      0,
      0
    );
    gl.uniform2f(cache.scaleLocation, context.scaleX, context.scaleY);
    gl.uniform2f(cache.offsetLocation, context.offsetX, context.offsetY);
    gl.drawArrays(gl.TRIANGLES, 0, count);
    gl.flush();
    gl.deleteBuffer(coordsBuffer);
    gl.deleteBuffer(colorsBuffer);
    return canvas;
  }
  return {
    tryInitGL() {