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/jni/RenderEffect.cpp b/libs/hwui/jni/RenderEffect.cpp
index 213f35a..f3db170 100644
--- a/libs/hwui/jni/RenderEffect.cpp
+++ b/libs/hwui/jni/RenderEffect.cpp
@@ -15,6 +15,7 @@
  */
 #include "Bitmap.h"
 #include "GraphicsJNI.h"
+#include "SkBlendMode.h"
 #include "SkImageFilter.h"
 #include "SkImageFilters.h"
 #include "graphics_jni_helpers.h"