add assert that the lock-count on pixelref is balanced

BUG=skia:
TBR=

Review URL: https://codereview.chromium.org/1147153004
diff --git a/tests/CachedDecodingPixelRefTest.cpp b/tests/CachedDecodingPixelRefTest.cpp
index 670d849..66e5273 100644
--- a/tests/CachedDecodingPixelRefTest.cpp
+++ b/tests/CachedDecodingPixelRefTest.cpp
@@ -262,11 +262,13 @@
 
 // new/lock/delete is an odd pattern for a pixelref, but it needs to not assert
 static void test_newlockdelete(skiatest::Reporter* reporter) {
+#ifdef SK_SUPPORT_LEGACY_UNBALANCED_PIXELREF_LOCKCOUNT
     SkBitmap bm;
     SkImageGenerator* ig = new TestImageGenerator(
         TestImageGenerator::kSucceedGetPixels_TestType, reporter);
     SkInstallDiscardablePixelRef(ig, &bm);
     bm.pixelRef()->lockPixels();
+#endif
 }
 
 /**