[PDF] Fix shader fallback mapping when clipped

The bounding box used for our pattern sizing is in device coordinates,
but SkPDFImageShader::Create() runs it through the inverse CTM to map
into shader space (with a notable effect of vertical flipping).

In order not to implode, the fallback shader path needs to compute its
adjustments in a consistent space.

BUG=skia:3398, chromium:454591, chromium:455052
R=halcanary@google.com

Review URL: https://codereview.chromium.org/901303003
1 file changed