Adds debug printing of units in unit tests.

Bug: webrtc:9656
Change-Id: I643b79bc214643f47b2b64967ce713665dbef5c9
Reviewed-on: https://webrtc-review.googlesource.com/95652
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24436}
diff --git a/api/units/timestamp.h b/api/units/timestamp.h
index 1b5e84f..6e5e392 100644
--- a/api/units/timestamp.h
+++ b/api/units/timestamp.h
@@ -11,6 +11,10 @@
 #ifndef API_UNITS_TIMESTAMP_H_
 #define API_UNITS_TIMESTAMP_H_
 
+#ifdef UNIT_TEST
+#include <ostream>  // no-presubmit-check TODO(webrtc:8982)
+#endif              // UNIT_TEST
+
 #include <stdint.h>
 #include <limits>
 #include <string>
@@ -203,6 +207,14 @@
 
 std::string ToString(const Timestamp& value);
 
+#ifdef UNIT_TEST
+inline std::ostream& operator<<(  // no-presubmit-check TODO(webrtc:8982)
+    std::ostream& stream,         // no-presubmit-check TODO(webrtc:8982)
+    Timestamp value) {
+  return stream << ToString(value);
+}
+#endif  // UNIT_TEST
+
 }  // namespace webrtc
 
 #endif  // API_UNITS_TIMESTAMP_H_