Make GrGpuCommandBuffer infer its render target from first draw

This is a temporary workaround to allow removal of GrBatch::renderTarget().

Change-Id: Ic14710a369802064cf6446e8191a98ea3595556d
Reviewed-on: https://skia-review.googlesource.com/5342
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
diff --git a/src/gpu/GrRenderTargetOpList.cpp b/src/gpu/GrRenderTargetOpList.cpp
index aab71f9..b69d915 100644
--- a/src/gpu/GrRenderTargetOpList.cpp
+++ b/src/gpu/GrRenderTargetOpList.cpp
@@ -204,8 +204,7 @@
                 static const GrGpuCommandBuffer::LoadAndStoreInfo kBasicLoadStoreInfo
                     { GrGpuCommandBuffer::LoadOp::kLoad,GrGpuCommandBuffer::StoreOp::kStore,
                       GrColor_ILLEGAL };
-                commandBuffer.reset(fGpu->createCommandBuffer(currentRT,
-                                                              kBasicLoadStoreInfo,   // Color
+                commandBuffer.reset(fGpu->createCommandBuffer(kBasicLoadStoreInfo,   // Color
                                                               kBasicLoadStoreInfo)); // Stencil
             }
             flushState->setCommandBuffer(commandBuffer.get());