IWYU for gms.

This almost gets gms to be iwyu clean. The last bit is around gm.cpp
and the tracing framework and its use of atomic. Will also need a way
of keeping things from regressing, which is difficult due to needing to
do this outside-in.

Change-Id: I1393531e99da8b0f1a29f55c53c86d53f459af7d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/211593
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
diff --git a/gm/drawregion.cpp b/gm/drawregion.cpp
index ff06d1f..0f9dcc9 100644
--- a/gm/drawregion.cpp
+++ b/gm/drawregion.cpp
@@ -7,7 +7,11 @@
 
 #include "gm/gm.h"
 #include "include/core/SkCanvas.h"
+#include "include/core/SkPaint.h"
+#include "include/core/SkRect.h"
 #include "include/core/SkRegion.h"
+#include "include/core/SkSize.h"
+#include "include/core/SkString.h"
 
 /**
  *  This is very similar to the RectGrid macrobench in Android.