constructor() {
    this.alpha = false;
    this.brightness = false;
    this.contrast = false;
    this.hue = false;
    this.saturation = false;
    this.gamma = false;
    this.colorToAlpha = false;
  }
A class containing a set of flags indicating which parts of an
<code>ImageryLayer</code> need to be processed.

This is used in the <code>ImageryPipelineStage</code> to decide the
structure of the function that blends the imagery texture information
with the previous pixels.

Each flag indicates that at least one of the <code>ImageryLayer</code> objects
that are part of the input did <b>not</b> have the default value that
was defined via the corresponding <code>ImageryLayer.DEFAULT_...</code>>.

Note that the type of the flags can be <code>boolean</code> or
<code>number</code>. Users should check for these flags having
a 'truthy' or 'falsy' value.

@private