sql: add missing sql_export.h to the corresponding BUILD.gn file

sql/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//testing/test.gni")
 
 component("sql") {
   sources = [
     "connection.cc",
     "connection.h",
     "connection_memory_dump_provider.cc",
     "connection_memory_dump_provider.h",
     "error_delegate_util.cc",
     "error_delegate_util.h",
     "init_status.h",
     "meta_table.cc",
     "meta_table.h",
     "recovery.cc",
     "recovery.h",
+    "sql_export.h",
     "sql_memory_dump_provider.cc",
     "sql_memory_dump_provider.h",
     "statement.cc",
     "statement.h",
     "transaction.cc",
     "transaction.h",
     "vfs_wrapper.cc",
     "vfs_wrapper.h",
   ]
 
@@ skipping 88 matching lines @@
   deps = [
     ":redirection_header",
     ":sql",
     ":sql_unittests_bundle_data",
     ":test_support",
     "//base/test:test_support",
     "//testing/gtest",
     "//third_party/sqlite",
   ]
 }