为什么“webgl”上下文不适用于Chrome？

Question

这段代码在Chrome上返回null，但会在Firefox上返回正确的上下文。

var create3DContext = function(canvas, opt_attribs) {
  var names = ["webgl", "experimental-webgl"];
  var context = null;
  for (var ii = 0; ii < names.length; ++ii) {
    try {
      context = canvas.getContext(names[ii], opt_attribs);
    } catch(e) {}
    if (context) {
      break;
    }
  }
  return context;
}

这就是它的名称：

var setupWebGL = function(canvas, opt_attribs) {
  function showLink(str) {
    var container = canvas.parentNode;
    if (container) {
      container.innerHTML = makeFailHTML(str);
    }
  };

  if (!window.WebGLRenderingContext) {
    showLink(GET_A_WEBGL_BROWSER);
    return null;
  }

  var context = create3DContext(canvas, opt_attribs);
  if (!context) {
    showLink(OTHER_PROBLEM);
  }
  return context;
};

var getWebGLContext = function(canvas, opt_attribs) {
  if (isInIFrame()) {
    updateCSSIfInIFrame();

    // make the canvas backing store the size it's displayed.
    canvas.width = canvas.clientWidth;
    canvas.height = canvas.clientHeight;
  } else {
    var title = document.title;
    var h1 = document.createElement("h1");
    h1.innerText = title;
    document.body.insertBefore(h1, document.body.children[0]);
  }

  var gl = setupWebGL(canvas, opt_attribs);
  return gl;
};

var isInIFrame = function() {
  return window != window.top;
};


getWebGLContext(document.getElementById("canvas"));