Move GrFixedClip into src directory

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2254343003

Review-Url: https://codereview.chromium.org/2254343003
diff --git a/src/gpu/GrClipStackClip.cpp b/src/gpu/GrClipStackClip.cpp
index 975f56a..695eda9 100644
--- a/src/gpu/GrClipStackClip.cpp
+++ b/src/gpu/GrClipStackClip.cpp
@@ -10,6 +10,7 @@
 #include "GrAppliedClip.h"
 #include "GrDrawingManager.h"
 #include "GrDrawContextPriv.h"
+#include "GrFixedClip.h"
 #include "GrGpuResourcePriv.h"
 #include "GrRenderTargetPriv.h"
 #include "GrStencilAttachment.h"