Move GCTracer to separate files.

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.
 
 # TODO(jochen): These will need to be user-settable to support standalone V8
 # builds.
 v8_compress_startup_data = "off"
 v8_deprecation_warnings = false
 v8_enable_disassembler = false
 v8_enable_gdbjit = false
@@ skipping 525 matching lines @@
     "src/flag-definitions.h",
     "src/flags.cc",
     "src/flags.h",
     "src/frames-inl.h",
     "src/frames.cc",
     "src/frames.h",
     "src/full-codegen.cc",
     "src/full-codegen.h",
     "src/func-name-inferrer.cc",
     "src/func-name-inferrer.h",
+    "src/gc-tracer.cc",
+    "src/gc-tracer.h",
     "src/gdb-jit.cc",
     "src/gdb-jit.h",
     "src/global-handles.cc",
     "src/global-handles.h",
     "src/globals.h",
     "src/handles-inl.h",
     "src/handles.cc",
     "src/handles.h",
     "src/hashmap.h",
     "src/heap-inl.h",
@@ skipping 620 matching lines @@
     deps = [
       ":v8_base",
       ":v8_nosnapshot",
     ]
   }
 
   direct_dependent_configs = [ ":external_config" ]
 }
 
 }