Expose WriteBatch::Append in the C API.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=209345072

db/c.cc

@@ -359,7 +359,7 @@ void leveldb_writebatch_delete(
 }
 
 void leveldb_writebatch_iterate(
-    leveldb_writebatch_t* b,
+    const leveldb_writebatch_t* b,
     void* state,
     void (*put)(void*, const char* k, size_t klen, const char* v, size_t vlen),
     void (*deleted)(void*, const char* k, size_t klen)) {
@@ -382,6 +382,11 @@ void leveldb_writebatch_iterate(
   b->rep.Iterate(&handler);
 }
 
+void leveldb_writebatch_append(leveldb_writebatch_t *destination,
+                               const leveldb_writebatch_t *source) {
+  destination->rep.Append(source->rep);
+}
+
 leveldb_options_t* leveldb_options_create() {
   return new leveldb_options_t;
 }

db/c_test.c

@@ -228,12 +228,18 @@ int main(int argc, char** argv) {
     leveldb_writebatch_clear(wb);
     leveldb_writebatch_put(wb, "bar", 3, "b", 1);
     leveldb_writebatch_put(wb, "box", 3, "c", 1);
-    leveldb_writebatch_delete(wb, "bar", 3);
+
+    leveldb_writebatch_t* wb2 = leveldb_writebatch_create();
+    leveldb_writebatch_delete(wb2, "bar", 3);
+    leveldb_writebatch_append(wb, wb2);
+    leveldb_writebatch_destroy(wb2);
+
     leveldb_write(db, woptions, wb, &err);
     CheckNoError(err);
     CheckGet(db, roptions, "foo", "hello");
     CheckGet(db, roptions, "bar", NULL);
     CheckGet(db, roptions, "box", "c");
+
     int pos = 0;
     leveldb_writebatch_iterate(wb, &pos, CheckPut, CheckDel);
     CheckCondition(pos == 3);

include/leveldb/c.h

@@ -155,9 +155,11 @@ LEVELDB_EXPORT void leveldb_writebatch_put(leveldb_writebatch_t*,
 LEVELDB_EXPORT void leveldb_writebatch_delete(leveldb_writebatch_t*,
                                               const char* key, size_t klen);
 LEVELDB_EXPORT void leveldb_writebatch_iterate(
-    leveldb_writebatch_t*, void* state,
+    const leveldb_writebatch_t*, void* state,
     void (*put)(void*, const char* k, size_t klen, const char* v, size_t vlen),
     void (*deleted)(void*, const char* k, size_t klen));
+LEVELDB_EXPORT void leveldb_writebatch_append(
+    leveldb_writebatch_t* destination, const leveldb_writebatch_t* source);
 
 /* Options */