Use SkMakeBitmapShader, avoid bitmap copy

CreateBitmapShader now forces a copy. This updates the call sites
to use SkMakeBitmapShader (in SkImagePriv.h) with
kNever_SkCopyPixelsMode.

This maintains the behavior where apps can modify the bitmap in
the shader after creating the shader.

This also ensures that the texture cache will work (since it's
based off of SkPixelRefs).

BUG:31594626
Change-Id: Ic75cb6cdc05c750b7946208e48a8127838d9c2f8