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/tests/common/CallCountingCanvas.h b/libs/hwui/tests/common/CallCountingCanvas.h
index d3c41191..dc36a2e 100644
--- a/libs/hwui/tests/common/CallCountingCanvas.h
+++ b/libs/hwui/tests/common/CallCountingCanvas.h
@@ -19,6 +19,8 @@
 #include <SkCanvasVirtualEnforcer.h>
 #include <SkNoDrawCanvas.h>
 
+enum class SkBlendMode;
+
 namespace android {
 namespace uirenderer {
 namespace test {