GOLD: workaround static constexpr linking problem with SkImageFilters::CropRect::kNoCropRect

Skia linking fails in GOLD because of missing instanciation of kNoCropRect
in SkImageFilters::CropRect. This breaks compilation of skia_renderer
service. More details of this kind of issue in GOLD can be seen in
https://chromium-review.googlesource.com/c/chromium/src/+/2436824

To workaround this, we move the declaration from being a member of
a struct to a namespace constexpr.

bug: chromium:819294
Change-Id: I52e98be440d05236df886b6ff83b84f29cbe7edd
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/335537
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
2 files changed