Track nested picture xform state for layer hoisting

The accumulated matrix state of any enclosing SkPictures must be stored separate from the picture-local CTM. Any setMatrix calls inside a layer need to replace the picture-local CTM but concatenate with the enclosing SkPicture transform state (and the transform state needed to translate the layer to the correct location in the cached GrTexture).

Review URL: https://codereview.chromium.org/639863005
7 files changed