Cleanup references to AHardwareBuffer to match NDK declarations.

Change-Id: Iaf796be04a5ac04873d420960238ea06294518f7
Reviewed-on: https://skia-review.googlesource.com/60240
Reviewed-by: Stan Iliev <stani@google.com>
Commit-Queue: Derek Sollenberger <djsollen@google.com>
diff --git a/src/gpu/GrAHardwareBufferImageGenerator.h b/src/gpu/GrAHardwareBufferImageGenerator.h
index e1814f8..6f51700 100644
--- a/src/gpu/GrAHardwareBufferImageGenerator.h
+++ b/src/gpu/GrAHardwareBufferImageGenerator.h
@@ -9,7 +9,9 @@
 
 #include "SkImageGenerator.h"
 
-struct AHardwareBuffer;
+extern "C" {
+    typedef struct AHardwareBuffer AHardwareBuffer;
+}
 
 /**
  *  GrAHardwareBufferImageGenerator allows to create an SkImage attached to