URLFetcher won't call delegate until file is closed.

net/base/file_stream_context_win.cc

Index: net/base/file_stream_context_win.cc
diff --git a/net/base/file_stream_context_win.cc b/net/base/file_stream_context_win.cc
index 5fb30859e7559996f8d65b4ee52473089ed1dedd..4a666c70a5b98d746e0af948669b74dfbf0d6e80 100644
--- a/net/base/file_stream_context_win.cc
+++ b/net/base/file_stream_context_win.cc
@@ -196,6 +196,15 @@ FileStream::Context::IOResult FileStream::Context::FlushFileImpl() {
   return IOResult::FromOSError(GetLastError());
 }
 
+FileStream::Context::IOResult FileStream::Context::CloseFileImpl() {
+  bool success = base::ClosePlatformFile(file_);
+  file_ = base::kInvalidPlatformFileValue;
+  if (success)
+    return IOResult(OK, 0);
+
+  return IOResult::FromOSError(GetLastError());
+}
+
 void FileStream::Context::IOCompletionIsPending(
     const CompletionCallback& callback,
     IOBuffer* buf) {