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/CanvasTransform.cpp b/libs/hwui/CanvasTransform.cpp
index 673041a..cd4fae8 100644
--- a/libs/hwui/CanvasTransform.cpp
+++ b/libs/hwui/CanvasTransform.cpp
@@ -17,6 +17,7 @@
 #include "CanvasTransform.h"
 
 #include <SkAndroidFrameworkUtils.h>
+#include <SkBlendMode.h>
 #include <SkColorFilter.h>
 #include <SkGradientShader.h>
 #include <SkHighContrastFilter.h>