IWYU -- SkShader.h

Bug: skia:
Change-Id: I57bffc14c4888627a22158e35f3ac3b762138f02
Reviewed-on: https://skia-review.googlesource.com/98520
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/src/shaders/SkShaderBase.h b/src/shaders/SkShaderBase.h
index 8831878..f72863e 100644
--- a/src/shaders/SkShaderBase.h
+++ b/src/shaders/SkShaderBase.h
@@ -9,6 +9,7 @@
 #define SkShaderBase_DEFINED
 
 #include "SkFilterQuality.h"
+#include "SkMask.h"
 #include "SkMatrix.h"
 #include "SkShader.h"