Reland of Initial version of file wrapper

webrtc/base/BUILD.gn

Index: webrtc/base/BUILD.gn
diff --git a/webrtc/base/BUILD.gn b/webrtc/base/BUILD.gn
index e166a4f7ba3f45274d33fd8e89b099196df1dc3e..8630d2beeb75176808a3949c1fae2652a328ccb1 100644
--- a/webrtc/base/BUILD.gn
+++ b/webrtc/base/BUILD.gn
@@ -124,6 +124,8 @@ static_library("rtc_base_approved") {
     "event_tracer.h",
     "exp_filter.cc",
     "exp_filter.h",
+    "file.cc",
+    "file.h",
     "format_macros.h",
     "location.cc",
     "location.h",
@@ -176,6 +178,14 @@ static_library("rtc_base_approved") {
     libs += [ "log" ]
   }
 
+  if (is_posix) {
+    sources += [ "file_posix.cc" ]
+  }
+
+  if (is_win) {
+    sources += [ "file_win.cc" ]
+  }
+
   if (build_with_chromium) {
     # Dependency on chromium's logging (in //base).
     deps += [ "//base:base" ]