s/gpr_slice/grpc_slice, and move around tests, impls
diff --git a/include/grpc/impl/codegen/slice.h b/include/grpc/impl/codegen/slice.h
index a2637ee..79297ce 100644
--- a/include/grpc/impl/codegen/slice.h
+++ b/include/grpc/impl/codegen/slice.h
@@ -35,6 +35,72 @@
 #define GRPC_IMPL_CODEGEN_SLICE_H
 
 #include <stddef.h>
+#include <stdint.h>
+
+/* Slice API
+
+   A slice represents a contiguous reference counted array of bytes.
+   It is cheap to take references to a slice, and it is cheap to create a
+   slice pointing to a subset of another slice.
+
+   The data-structure for slices is exposed here to allow non-gpr code to
+   build slices from whatever data they have available.
+
+   When defining interfaces that handle slices, care should be taken to define
+   reference ownership semantics (who should call unref?) and mutability
+   constraints (is the callee allowed to modify the slice?) */
+
+/* Reference count container for grpc_slice. Contains function pointers to
+   increment and decrement reference counts. Implementations should cleanup
+   when the reference count drops to zero.
+   Typically client code should not touch this, and use grpc_slice_malloc,
+   grpc_slice_new, or grpc_slice_new_with_len instead. */
+typedef struct grpc_slice_refcount {
+  void (*ref)(void *);
+  void (*unref)(void *);
+} grpc_slice_refcount;
+
+#define GPR_SLICE_INLINED_SIZE (sizeof(size_t) + sizeof(uint8_t *) - 1)
+
+/* A grpc_slice s, if initialized, represents the byte range
+   s.bytes[0..s.length-1].
+
+   It can have an associated ref count which has a destruction routine to be run
+   when the ref count reaches zero (see grpc_slice_new() and grp_slice_unref()).
+   Multiple grpc_slice values may share a ref count.
+
+   If the slice does not have a refcount, it represents an inlined small piece
+   of data that is copied by value. */
+typedef struct grpc_slice {
+  struct grpc_slice_refcount *refcount;
+  union {
+    struct {
+      uint8_t *bytes;
+      size_t length;
+    } refcounted;
+    struct {
+      uint8_t length;
+      uint8_t bytes[GPR_SLICE_INLINED_SIZE];
+    } inlined;
+  } data;
+} grpc_slice;
+
+#define GRPC_SLICE_BUFFER_INLINE_ELEMENTS 8
+
+/* Represents an expandable array of slices, to be interpreted as a
+   single item. */
+typedef struct {
+  /* slices in the array */
+  grpc_slice *slices;
+  /* the number of slices in the array */
+  size_t count;
+  /* the number of slices allocated in the array */
+  size_t capacity;
+  /* the combined length of all slices in the array */
+  size_t length;
+  /* inlined elements to avoid allocations */
+  grpc_slice inlined[GRPC_SLICE_BUFFER_INLINE_ELEMENTS];
+} grpc_slice_buffer;
 
 #define GPR_SLICE_START_PTR(slice)                  \
   ((slice).refcount ? (slice).data.refcounted.bytes \