Reland 28629004: adding new AEC dump start interface for chrome.

This is required because we are not allow to pass CRT objects across dll boundaries, that says, when we pass a file descriptor from chrome dll to libpeerconnection dll, the file descriptor will become invalid immediate, more information can be found here:
http://msdn.microsoft.com/en-us/library/ms235460.aspx

R=andresp@webrtc.org, andrew@webrtc.org, bjornv@webrtc.org, henrike@webrtc.org, henrikg@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/30629004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7418 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/base/platform_file.h

@@ -0,0 +1,44 @@
+/*
+ *  Copyright 2014 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_BASE_PLATFORM_FILE_H_
+#define WEBRTC_BASE_PLATFORM_FILE_H_
+
+#include <stdio.h>
+
+#if defined(WEBRTC_WIN)
+#include <windows.h>
+#endif
+
+namespace rtc {
+
+#if defined(WEBRTC_WIN)
+typedef HANDLE PlatformFile;
+#elif defined(WEBRTC_POSIX)
+typedef int PlatformFile;
+#else
+#error Unsupported platform
+#endif
+
+extern const PlatformFile kInvalidPlatformFileValue;
+
+// Associates a standard FILE stream with an existing PlatformFile.
+// Note that after this function has returned a valid FILE stream,
+// the PlatformFile should no longer be used.
+FILE* FdopenPlatformFileForWriting(PlatformFile file);
+
+// Closes a PlatformFile.
+// Don't use ClosePlatformFile to close a file opened with FdopenPlatformFile.
+// Use fclose instead.
+bool ClosePlatformFile(PlatformFile file);
+
+}  // namespace rtc
+
+#endif  // WEBRTC_BASE_PLATFORM_FILE_H_