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/skbug_5321.cpp b/gm/skbug_5321.cpp
index 73fb268..3ad71af 100644
--- a/gm/skbug_5321.cpp
+++ b/gm/skbug_5321.cpp
@@ -6,8 +6,15 @@
  */
 
 #include "gm/gm.h"
+#include "include/core/SkCanvas.h"
+#include "include/core/SkFont.h"
+#include "include/core/SkFontTypes.h"
+#include "include/core/SkPaint.h"
+#include "include/core/SkScalar.h"
 #include "include/core/SkTextBlob.h"
 
+#include <string.h>
+
 // https://bugs.skia.org/5321
 // two strings should draw the same.  PDF did not.
 DEF_SIMPLE_GM(skbug_5321, canvas, 128, 128) {