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/pipeline/skia/StretchMask.cpp b/libs/hwui/pipeline/skia/StretchMask.cpp
index 2dbeb3a..b169c92 100644
--- a/libs/hwui/pipeline/skia/StretchMask.cpp
+++ b/libs/hwui/pipeline/skia/StretchMask.cpp
@@ -14,8 +14,10 @@
  * limitations under the License.
  */
 #include "StretchMask.h"
-#include "SkSurface.h"
+
+#include "SkBlendMode.h"
 #include "SkCanvas.h"
+#include "SkSurface.h"
 #include "TransformCanvas.h"
 #include "SkiaDisplayList.h"