Record UMA statistics for file_stream operations.

net/base/file_stream_metrics.h

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// This file defines FileStream, a basic interface for reading and writing files

[cbentzel, 2011/08/16 13:36:02]

This comment is wrong.

+// synchronously or asynchronously with support for seeking to an offset.
+// Note that even when used asynchronously, only one operation is supported at
+// a time.
+
+#ifndef NET_BASE_FILE_STREAM_METRICS_H_
+#define NET_BASE_FILE_STREAM_METRICS_H_
+#pragma once
+
+namespace net {
+
+enum FileErrorSource {
+  FILE_ERROR_SOURCE_IS_NOT_OPEN = 0,
+  FILE_ERROR_SOURCE_OPEN,
+  FILE_ERROR_SOURCE_WRITE,
+  FILE_ERROR_SOURCE_READ,
+  FILE_ERROR_SOURCE_SEEK,
+  FILE_ERROR_SOURCE_FLUSH,
+  FILE_ERROR_SOURCE_SET_EOF,
+  FILE_ERROR_SOURCE_GET_SIZE,
+  FILE_ERROR_SOURCE_COUNT,
+};
+
+// UMA error statistics gathering.
+int ReduceErrorRange(int error);
+int MaxError();
+void RecordFileError(int error, FileErrorSource type);

[cbentzel, 2011/08/16 13:36:02]

After seeing this be used, may be easier to change the signature to 

RecordFileError(int error, FileErrorSource type, bool record);

Also, you should document what |error| is - in this case, it is an errno/HRESULT
style error rather than a net error. 

[cbentzel, 2011/08/16 13:36:02]

In Win, this is actually a DWORD for error. DWORD is an unsigned long. Yes,
probably can cast to an int but may be worth some additional consideration.

errno is an int on the errno.h's I've seen - may be specified by OpenGroup as
well.

[ahendrickson, 2011/08/17 20:12:04]

Done.

[ahendrickson, 2011/08/17 20:12:04]

On Win, I mask out the 16 high bits anyway, so it doesn't matter if it's signed
or not.

+
+}  // namespace net
+
+#endif  // NET_BASE_FILE_STREAM_METRICS_H_