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/simple_magnification.cpp b/gm/simple_magnification.cpp
index b942632..3c0a636 100644
--- a/gm/simple_magnification.cpp
+++ b/gm/simple_magnification.cpp
@@ -6,10 +6,28 @@
  */
 
 #include "gm/gm.h"
+#include "include/core/SkBitmap.h"
+#include "include/core/SkCanvas.h"
+#include "include/core/SkColor.h"
 #include "include/core/SkColorPriv.h"
+#include "include/core/SkImage.h"
+#include "include/core/SkImageFilter.h"
+#include "include/core/SkImageInfo.h"
+#include "include/core/SkPaint.h"
+#include "include/core/SkPoint.h"
+#include "include/core/SkRect.h"
+#include "include/core/SkRefCnt.h"
+#include "include/core/SkSize.h"
+#include "include/core/SkString.h"
 #include "include/core/SkSurface.h"
+#include "include/core/SkTypes.h"
 #include "include/effects/SkImageSource.h"
 #include "include/effects/SkMagnifierImageFilter.h"
+#include "include/gpu/GrTypes.h"
+
+#include <utility>
+
+class GrContext;
 
 static sk_sp<SkImage> make_image(GrContext* context, int size, GrSurfaceOrigin origin) {
     if (context) {