Add an SkImage::isProtected entry point

Android needs something like this to correctly pass an isProtected flag to SkSurfaces::RenderTarget. To be specific, they create a, possibly protected, image and then pass it to their Kawase blur code. The Kawase code then needs to create an appropriate SkSurface.

Change-Id: I1e193254bf59ab5963798dbc710cbc90f8248059
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/739456
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
16 files changed