SkOnce: add option to call another cleanup function once at exit.

tests/CachedDecodingPixelRefTest.cpp

Index: tests/CachedDecodingPixelRefTest.cpp
diff --git a/tests/CachedDecodingPixelRefTest.cpp b/tests/CachedDecodingPixelRefTest.cpp
index d725ff5fc9c57b7390f0ced1ca77f4f80f17dd5c..9ac5f8139259f2261e5fb98a5d6be76ada9b6dab 100644
--- a/tests/CachedDecodingPixelRefTest.cpp
+++ b/tests/CachedDecodingPixelRefTest.cpp
@@ -142,12 +142,6 @@ static void test_three_encodings(skiatest::Reporter* reporter,
     }
 }
 
-static void purge_global_scaled_image_cache() {
-    size_t byteLimit = SkScaledImageCache::GetByteLimit();
-    SkScaledImageCache::SetByteLimit(0);
-    SkScaledImageCache::SetByteLimit(byteLimit);
-}
-
 ////////////////////////////////////////////////////////////////////////////////
 static bool install_skCachingPixelRef(SkData* encoded, SkBitmap* dst) {
     return SkCachingPixelRef::Install(
@@ -169,7 +163,6 @@ static bool install_skDiscardablePixelRef(SkData* encoded, SkBitmap* dst) {
  */
 DEF_TEST(DecodingImageGenerator, reporter) {
     test_three_encodings(reporter, install_skCachingPixelRef);
-    purge_global_scaled_image_cache();
     test_three_encodings(reporter, install_skDiscardablePixelRef);
 }
 
@@ -302,8 +295,6 @@ DEF_TEST(DiscardableAndCachingPixelRef, reporter) {
     check_pixelref(TestImageGenerator::kSucceedGetPixels_TestType,
                    reporter, kSkCaching_PixelRefType, NULL);
 
-    purge_global_scaled_image_cache();
-
     check_pixelref(TestImageGenerator::kFailGetInfo_TestType,
                    reporter, kSkDiscardable_PixelRefType, NULL);
     check_pixelref(TestImageGenerator::kFailGetPixels_TestType,