Don't issue texture barriers for RT's with separate storage

src/gpu/GrTargetCommands.h

Index: src/gpu/GrTargetCommands.h
diff --git a/src/gpu/GrTargetCommands.h b/src/gpu/GrTargetCommands.h
index 5e35e50bbf3c7772a992e5d8bb83c4d08b78fdcd..2f9909bb026ae5bb3329a6f4d7946ecc86cf5291 100644
--- a/src/gpu/GrTargetCommands.h
+++ b/src/gpu/GrTargetCommands.h
@@ -242,11 +242,17 @@ private:
     };
 
     struct XferBarrier : public Cmd {
-        XferBarrier() : Cmd(kXferBarrier_CmdType) {}
+        XferBarrier(GrRenderTarget* rt)
+            : Cmd(kXferBarrier_CmdType)
+            , fRenderTarget(rt) {
+        }
 
         void execute(GrGpu*) override;
 
         GrXferBarrierType   fBarrierType;
+
+    private:
+        GrPendingIOResource<GrRenderTarget, kWrite_GrIOType> fRenderTarget;
     };
 
     static const int kCmdBufferInitialSizeInBytes = 8 * 1024;