Add WriteIsolatedOutput() functions

webrtc/test/testsupport/isolated_output.h

Index: webrtc/test/testsupport/isolated_output.h
diff --git a/webrtc/test/testsupport/isolated_output.h b/webrtc/test/testsupport/isolated_output.h
new file mode 100644
index 0000000000000000000000000000000000000000..f4e9695157101ae940d41387b9ee137028996675
--- /dev/null
+++ b/webrtc/test/testsupport/isolated_output.h
@@ -0,0 +1,35 @@
+/*
+ *  Copyright (c) 2016 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_TEST_TESTSUPPORT_ISOLATED_OUTPUT_H_
+#define WEBRTC_TEST_TESTSUPPORT_ISOLATED_OUTPUT_H_
+
+#include <stdlib.h>
+
+#include <string>
+
+namespace webrtc {
+namespace test {
+
+// Writes a |length| bytes array |buffer| to |filename| in isolated output
+// directory defined by swarming. If the file is existing, content will be
+// appended. Otherwise a new file will be created. This function returns false
+// if isolated output directory has not been defined, or |filename| indicates an
+// invalid or non-writable file, or underlying file system errors.
+bool WriteIsolatedOutput(const char* filename,
+                         const uint8_t* buffer,
+                         size_t length);
+
+bool WriteIsolatedOutput(const char* filename, const std::string& content);
+
+}  // namespace test
+}  // namespace webrtc
+
+#endif  // WEBRTC_TEST_TESTSUPPORT_ISOLATED_OUTPUT_H_