Change device creation to see the (optional) layer-paint

Motivation:

PDFDevice currently relies on 1) being told that the layer's paint has an imagefilter, and in the case, it creates a rasterdevice. It then relies on (2) canvas itself sniffing the layer's paint and offering to apply-the-imagefilter to call drawSprite instead of drawDevice.

This subtle interchange is fragile, and also does not support other unsupported PDF features like colorfilters. This CL is a step toward making this use-raster-instead-of-native approach to layers more completely in the subclass' hands.

Review URL: https://codereview.chromium.org/988413003
14 files changed