header self-sufficiency and idempotency

Change-Id: I4ec74a358e11d85c6eaf1658efd6f1391ee5e387
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/223930
Commit-Queue: Hal Canary <halcanary@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
Auto-Submit: Hal Canary <halcanary@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
diff --git a/src/gpu/GrContextThreadSafeProxyPriv.h b/src/gpu/GrContextThreadSafeProxyPriv.h
index bf09305..9f83e4b 100644
--- a/src/gpu/GrContextThreadSafeProxyPriv.h
+++ b/src/gpu/GrContextThreadSafeProxyPriv.h
@@ -10,6 +10,8 @@
 
 #include "include/gpu/GrContextThreadSafeProxy.h"
 
+#include "src/gpu/GrCaps.h"
+
 /**
  * Class that adds methods to GrContextThreadSafeProxy that are only intended for use internal to
  * Skia. This class is purely a privileged window into GrContextThreadSafeProxy. It should never