URLFetcher won't call delegate until file is closed.

net/base/file_stream_context_posix.cc

Index: net/base/file_stream_context_posix.cc
diff --git a/net/base/file_stream_context_posix.cc b/net/base/file_stream_context_posix.cc
index 1ef5be5fc16259364eedc03c63727953fc2dbe40..6e6bc6eaa698666b2245cbb32b28a91215fb3b8c 100644
--- a/net/base/file_stream_context_posix.cc
+++ b/net/base/file_stream_context_posix.cc
@@ -184,4 +184,13 @@ FileStream::Context::IOResult FileStream::Context::WriteFileImpl(
   return IOResult(res, 0);
 }
 
+FileStream::Context::IOResult FileStream::Context::CloseFileImpl() {
+  bool success = base::ClosePlatformFile(file_);
+  file_ = base::kInvalidPlatformFileValue;
+  if (!success)
+    return IOResult::FromOSError(errno);
+
+  return IOResult(OK, 0);
+}
+
 }  // namespace net