Minor refactor of GrLayerHoister

The main point of this CL is to make sure using the rect bounds (rather than the underlying texture's bounds) is acceptable in GrLayerHoister::FilterLayer.

This is split out of https://codereview.chromium.org/1943913002/ (Retract GrRenderTarget from GrLayerHoister)

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Review-Url: https://codereview.chromium.org/1947593002
2 files changed