Migrate PersistentCacheUtils logic into a cpp file.

This code is not performance-sensitive, and there doesn't seem to be any
benefit to making it header-only.

Change-Id: Ic83be5cbb96f08c18a144954be7453aaabaa5a72
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/394900
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
diff --git a/gn/gpu.gni b/gn/gpu.gni
index 6d5c88b..c5cdddb 100644
--- a/gn/gpu.gni
+++ b/gn/gpu.gni
@@ -149,6 +149,8 @@
   "$_src/gpu/GrPathRenderer.h",
   "$_src/gpu/GrPathRendererChain.cpp",
   "$_src/gpu/GrPathRendererChain.h",
+  "$_src/gpu/GrPersistentCacheUtils.cpp",
+  "$_src/gpu/GrPersistentCacheUtils.h",
   "$_src/gpu/GrPipeline.cpp",
   "$_src/gpu/GrPipeline.h",
   "$_src/gpu/GrPixmap.h",