Avoid creating full screen clear batches when there is already one in the queue.

src/gpu/GrDrawContext.cpp

Index: src/gpu/GrDrawContext.cpp
diff --git a/src/gpu/GrDrawContext.cpp b/src/gpu/GrDrawContext.cpp
index 0a6ab5b52704876ff8976489db3ecc114d3f8a2a..4096518f0003f6a56bff2c424a904785bf67a1e3 100644
--- a/src/gpu/GrDrawContext.cpp
+++ b/src/gpu/GrDrawContext.cpp
@@ -233,7 +233,7 @@ void GrDrawContext::clear(const SkIRect* rect,
     } else if (isFull) {
         this->getDrawTarget()->fullClear(this->accessRenderTarget(), color);
     } else {
-        sk_sp<GrBatch> batch = GrClearBatch::Make(*rect, color, this->accessRenderTarget());
+        sk_sp<GrBatch> batch(GrClearBatch::Make(*rect, color, this->accessRenderTarget()));
         this->getDrawTarget()->addBatch(std::move(batch));
     }
 }