Fix forward declare of GrDirectContext

Follow-up to https://skia-review.googlesource.com/c/skia/+/656237

Change-Id: Ifb1282375fa81fd2e18f8c8e65641e1fc6df28b0
diff --git a/libs/hwui/pipeline/skia/ShaderCache.h b/libs/hwui/pipeline/skia/ShaderCache.h
index f5506d6..0492d70 100644
--- a/libs/hwui/pipeline/skia/ShaderCache.h
+++ b/libs/hwui/pipeline/skia/ShaderCache.h
@@ -24,6 +24,7 @@
 #include <string>
 #include <vector>
 
+class GrDirectContext;
 class SkData;
 
 namespace android {