EXPERIMENT: Increase grpc_slice size to allow more inlining

include/grpc/impl/codegen/slice.h

@@ -62,7 +62,12 @@ typedef struct grpc_slice_refcount {
   struct grpc_slice_refcount *sub_refcount;
 } grpc_slice_refcount;
 
-#define GRPC_SLICE_INLINED_SIZE (sizeof(size_t) + sizeof(uint8_t *) - 1)
+/* Inlined half of grpc_slice is allowed to expand the size of the overall type
+   by this many bytes */
+#define GRPC_SLICE_INLINE_EXTRA_SIZE sizeof(void *)
+
+#define GRPC_SLICE_INLINED_SIZE \
+  (sizeof(size_t) + sizeof(uint8_t *) - 1 + GRPC_SLICE_INLINE_EXTRA_SIZE)
 
 /** A grpc_slice s, if initialized, represents the byte range
    s.bytes[0..s.length-1].