Always have GrLayer's rect be valid

This CL just makes atlasing easier/clearer since there is a separate atlased query method. Not using the rect as a signal also simplifies the rendering of the layer in SkGpuDevice.cpp.

This is calved off from (Add atlased layer purging - https://codereview.chromium.org/367073002/)

R=bsalomon@google.com

Author: robertphillips@google.com

Review URL: https://codereview.chromium.org/384233002
4 files changed