markDirty() {
    this.isDirty = true;
    if (typeof this._text === 'string' || this._parseTree !== undefined) {
      this._rawSrc = undefined;
    }
    this._md5Hex = undefined;
    if (this.isInline && this.assetGraph && this.incomingInlineRelation) {
      // Cascade dirtiness to containing asset and re-inline
      if (this.incomingInlineRelation.from !== this) {
        this.incomingInlineRelation.inline();
      }
    }
    return this;
  }
Sets the `dirty` flag of the asset, which is the way to say
that the asset has been manipulated since it was first loaded
(read from disc or loaded via http). For inline assets the flag
is set if the asset has been manipulated since it was last
synchronized with (copied into) its containing asset.

For assets that support a `text` or `parseTree` property, calling
`markDirty()` will invalidate any cached serializations of the
asset.

@return {Asset} The asset itself (chaining-friendly)