Collapse most spammy output of webrtc_perf_tests with PrintResultList

webrtc/test/testsupport/perf_test.h

Index: webrtc/test/testsupport/perf_test.h
diff --git a/webrtc/test/testsupport/perf_test.h b/webrtc/test/testsupport/perf_test.h
index 76e09e1cbba021ef299f876628d1d521992bcdab..6e49ac90e0e8653cc9550e88ef4fa1b1a8ce8f81 100644
--- a/webrtc/test/testsupport/perf_test.h
+++ b/webrtc/test/testsupport/perf_test.h
@@ -15,6 +15,7 @@
 #ifndef WEBRTC_TEST_TESTSUPPORT_PERF_TEST_H_
 #define WEBRTC_TEST_TESTSUPPORT_PERF_TEST_H_
 
+#include <sstream>
 #include <string>
 
 namespace webrtc {
@@ -116,6 +117,23 @@ std::string SystemCommitChargeToString(const std::string& test_name,
                                        size_t charge,
                                        bool important);
 
+// Converts list of values into comma-separated string for PrintResultList.
+template <typename Container>
+std::string ValuesToString(const Container& container) {
+  if (container.empty())
+    return "";
+
+  std::stringstream ss;
+  auto it = container.begin();
+  while (true) {
+    ss << *it;
+    if (++it == container.end())
+      break;
+    ss << ',';
+  }
+  return ss.str();
+}
+
 }  // namespace test
 }  // namespace webrtc