protected final BUILDER getThis() {
    return (BUILDER) this;
  }
Concrete builder classes should override this method to return a data source for the request.

<p>IMPORTANT: Do NOT ever call this method directly. This method is only to be called from a
supplier created in {#code getDataSourceSupplierForRequest(REQUEST, boolean)}.

<p>IMPORTANT: Make sure that you do NOT use any non-final field from this method, as the field
may change if the instance of this builder gets reused. If any such field is required, override
{#code getDataSourceSupplierForRequest(REQUEST, boolean)}, and store the field in a final
variable (same as it is done for callerContext).
drawee/src/main/java/com/facebook/drawee/controller/AbstractDraweeControllerBuilder.java