header self-sufficiency and idempotency

Change-Id: I4ec74a358e11d85c6eaf1658efd6f1391ee5e387
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/223930
Commit-Queue: Hal Canary <halcanary@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
Auto-Submit: Hal Canary <halcanary@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
diff --git a/src/gpu/mock/GrMockTexture.h b/src/gpu/mock/GrMockTexture.h
index d7aa866..ddf5e52 100644
--- a/src/gpu/mock/GrMockTexture.h
+++ b/src/gpu/mock/GrMockTexture.h
@@ -11,6 +11,7 @@
 #include "include/gpu/GrTexture.h"
 #include "include/gpu/mock/GrMockTypes.h"
 #include "src/gpu/GrRenderTargetPriv.h"
+#include "src/gpu/GrStencilAttachment.h"
 #include "src/gpu/GrTexturePriv.h"
 #include "src/gpu/mock/GrMockGpu.h"