Add granular file tracing.

base/BUILD.gn

 # Copyright (c) 2013 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/ui.gni")
 import("//testing/test.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
@@ skipping 198 matching lines @@
     "files/file_path_watcher_fsevents.cc",
     "files/file_path_watcher_fsevents.h",
     "files/file_path_watcher_kqueue.cc",
     "files/file_path_watcher_kqueue.h",
     "files/file_path_watcher_linux.cc",
     "files/file_path_watcher_mac.cc",
     "files/file_path_watcher_win.cc",
     "files/file_posix.cc",
     "files/file_proxy.cc",
     "files/file_proxy.h",
+    "files/file_tracing.cc",
+    "files/file_tracing.h",
     "files/file_util.cc",
     "files/file_util.h",
     "files/file_util_android.cc",
     "files/file_util_linux.cc",
     "files/file_util_mac.mm",
     "files/file_util_posix.cc",
     "files/file_util_proxy.cc",
     "files/file_util_proxy.h",
     "files/file_util_win.cc",
     "files/file_win.cc",
@@ skipping 1272 matching lines @@
 
   # GYP: //base.gyp:base_java_unittest_support
   android_library("base_java_unittest_support") {
     deps = [
       ":base_java",
     ]
     java_files =
         [ "test/android/java/src/org/chromium/base/ContentUriTestUtils.java" ]
   }
 }