Decouple root visitors from object visitors.

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("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/dcheck_always_on.gni")
 import("//build/config/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
@@ skipping 1931 matching lines @@
     "src/v8.cc",
     "src/v8.h",
     "src/v8memory.h",
     "src/v8threads.cc",
     "src/v8threads.h",
     "src/value-serializer.cc",
     "src/value-serializer.h",
     "src/vector.h",
     "src/version.cc",
     "src/version.h",
+    "src/visitors.cc",
+    "src/visitors.h",
     "src/vm-state-inl.h",
     "src/vm-state.h",
     "src/wasm/decoder.h",
     "src/wasm/function-body-decoder-impl.h",
     "src/wasm/function-body-decoder.cc",
     "src/wasm/function-body-decoder.h",
     "src/wasm/leb-helper.h",
     "src/wasm/module-decoder.cc",
     "src/wasm/module-decoder.h",
     "src/wasm/signature-map.cc",
@@ skipping 1284 matching lines @@
   ]
 
   configs = [
     ":external_config",
     ":internal_config_base",
   ]
 }
 
 v8_fuzzer("wasm_compile_fuzzer") {
 }