URLFetcher won't call delegate until file is closed.

net/base/file_stream.cc

Index: net/base/file_stream.cc
diff --git a/net/base/file_stream.cc b/net/base/file_stream.cc
index 85adaece3cd404aaf703330c1be77863e503e749..8e4558cbfebd84fefa002c29105888d9a7649201 100644
--- a/net/base/file_stream.cc
+++ b/net/base/file_stream.cc
@@ -93,6 +93,16 @@ int FileStream::OpenSync(const base::FilePath& path, int open_flags) {
   return context_->OpenSync(path, open_flags_);
 }
 
+int FileStream::Close(const CompletionCallback& callback) {
+  if (!is_async()) {
+    context_->CloseSync();
+    context_.reset();
+    return OK;
+  }
+  context_->CloseAsync(callback);
+  return ERR_IO_PENDING;
+}
+
 bool FileStream::IsOpen() const {
   return context_->file() != base::kInvalidPlatformFileValue;
 }