SkImageSource::Make() returns nullptr when srcrect is empty.

BUG=skia:6389
Change-Id: Ia995da1f70cbbc0c80ab76385f0ea8cc0d48fa07
Reviewed-on: https://skia-review.googlesource.com/9943
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
diff --git a/gn/tests.gni b/gn/tests.gni
index e086e0a..124be39 100644
--- a/gn/tests.gni
+++ b/gn/tests.gni
@@ -198,6 +198,7 @@
   "$_tests/SkBase64Test.cpp",
   "$_tests/SkBlend_optsTest.cpp",
   "$_tests/skbug5221.cpp",
+  "$_tests/skbug6389.cpp",
   "$_tests/SkColor4fTest.cpp",
   "$_tests/SkDOMTest.cpp",
   "$_tests/SkFixed15Test.cpp",