Default constructor for file

webrtc/base/file.cc

Index: webrtc/base/file.cc
diff --git a/webrtc/base/file.cc b/webrtc/base/file.cc
index c97504f9c737a438c1b2bd585e58bddb087810ed..74d48177e4b976ff27689e3e79c5a76f140beceb 100644
--- a/webrtc/base/file.cc
+++ b/webrtc/base/file.cc
@@ -14,6 +14,8 @@ namespace rtc {
 
 File::File(PlatformFile file) : file_(file) {}
 
+File::File() : file_(kInvalidPlatformFileValue) {}
+
 File::~File() {
   Close();
 }