Give GrSimpleMeshDrawOpHelper a cpp file

Change-Id: I1ac3f7d41d3d546801a7fc14008b801a11429472
Reviewed-on: https://skia-review.googlesource.com/22368
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
diff --git a/gn/gpu.gni b/gn/gpu.gni
index 253cf74..e61a907 100644
--- a/gn/gpu.gni
+++ b/gn/gpu.gni
@@ -278,6 +278,7 @@
   "$_src/gpu/ops/GrSemaphoreOp.h",
   "$_src/gpu/ops/GrShadowRRectOp.cpp",
   "$_src/gpu/ops/GrShadowRRectOp.h",
+  "$_src/gpu/ops/GrSimpleMeshDrawOpHelper.cpp",
   "$_src/gpu/ops/GrSimpleMeshDrawOpHelper.h",
   "$_src/gpu/ops/GrSmallPathRenderer.cpp",
   "$_src/gpu/ops/GrSmallPathRenderer.h",