checkColor = function(pixelContents, r, g, b) {
    context.readPixels(0, 0, 1, 1, goog.webgl.RGBA, goog.webgl.UNSIGNED_BYTE,
        pixelContents);
    assert.equal(pixelContents[0], r);
    assert.equal(pixelContents[1], g);
    assert.equal(pixelContents[2], b);
  }
Gets data for a single pixel and checks it against provided RGB values.
@param {Uint8Array} pixelContents Allocated space to store readPixel data.
@param {number} r Red value [0, 255]
@param {number} g Green value [0, 255]
@param {number} b Blue value [0, 255]