Added SkLRUCache.h and converted GPU program cache to use it.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4221

Change-Id: I7e4094c2f2a2ecc5909895a8a68b27047acdcbd0
Reviewed-on: https://skia-review.googlesource.com/4221
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
diff --git a/gn/tests.gni b/gn/tests.gni
index 8473e0e..5f2d8b7 100644
--- a/gn/tests.gni
+++ b/gn/tests.gni
@@ -117,6 +117,7 @@
   "$_tests/LayerDrawLooperTest.cpp",
   "$_tests/LayerRasterizerTest.cpp",
   "$_tests/LListTest.cpp",
+  "$_tests/LRUCacheTest.cpp",
   "$_tests/MallocPixelRefTest.cpp",
   "$_tests/MaskCacheTest.cpp",
   "$_tests/MathTest.cpp",