Add missing includes of SkBlendMode.h

It's being removed from SkPaint.h in https://skia-review.googlesource.com/c/skia/+/611077
and this was all the places I could find in frameworks/base.

We might need another CL for a few other Android repos.

Change-Id: I88d31166ed90356c4c52fbcde6bec6c1655b7cf2
diff --git a/libs/hwui/utils/PaintUtils.h b/libs/hwui/utils/PaintUtils.h
index 94bcb11..f44f9d0 100644
--- a/libs/hwui/utils/PaintUtils.h
+++ b/libs/hwui/utils/PaintUtils.h
@@ -19,6 +19,7 @@
 #include <GLES2/gl2.h>
 #include <utils/Blur.h>
 
+#include <SkBlendMode.h>
 #include <SkColorFilter.h>
 #include <SkPaint.h>
 #include <SkShader.h>