Add unit test to exercise GrTextureFreed message handling after a context abandon

Bug: 1011368, 1014993
Change-Id: Ie9f7be15b321daa05fcac8109a24e42810f10737
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249008
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/src/gpu/GrResourceCache.cpp b/src/gpu/GrResourceCache.cpp
index c7b91b9..6d9a961 100644
--- a/src/gpu/GrResourceCache.cpp
+++ b/src/gpu/GrResourceCache.cpp
@@ -635,6 +635,10 @@
 }
 
 void GrResourceCache::processFreedGpuResources() {
+    if (!fTexturesAwaitingUnref.count()) {
+      return;
+    }
+
     SkTArray<GrTextureFreedMessage> msgs;
     fFreedTextureInbox.poll(&msgs);
     for (int i = 0; i < msgs.count(); ++i) {