include what you use

BUG=skia:

Change-Id: I3b9fb3db06a26c55f338f05418ca8ba6fbe7cedf
Reviewed-on: https://skia-review.googlesource.com/8400
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/gm/clipdrawdraw.cpp b/gm/clipdrawdraw.cpp
index 389d7e3..59cf9da 100644
--- a/gm/clipdrawdraw.cpp
+++ b/gm/clipdrawdraw.cpp
@@ -6,6 +6,7 @@
  */
 
 #include "gm.h"
+#include "SkRegion.h"
 
 // This GM exercises the use case found in crbug.com/423834.
 // The following pattern: