Test abandoning GL context in dm/nanobench.

dm/DMTask.cpp

Index: dm/DMTask.cpp
diff --git a/dm/DMTask.cpp b/dm/DMTask.cpp
index d0a82b63d6d0bf29a94366a931c24700e3ffbb38..05eda4ea20386b62edbda7c784583d95f2d2bdb5 100644
--- a/dm/DMTask.cpp
+++ b/dm/DMTask.cpp
@@ -68,7 +68,10 @@ void GpuTask::run(GrContextFactory& factory) {
         this->start();
         if (!FLAGS_dryRun) this->draw(&factory);
         this->finish();
-        if (FLAGS_resetGpuContext) {
+        if (FLAGS_abandonGpuContext) {
+            factory.abandonContexts();
+        }
+        if (FLAGS_resetGpuContext || FLAGS_abandonGpuContext) {
             factory.destroyContexts();
         }
     }