Add a function to report perf results in JSON format.

Add support to report perf results in the JSON format specified in [1].

[1] https://github.com/catapult-project/catapult/blob/master/dashboard/docs/data-format.md


Bug: webrtc:8566
Change-Id: I25f829a4b012b3e2a3d56d61582a674f780148d0
Reviewed-on: https://webrtc-review.googlesource.com/26031
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Edward Lemur <ehmaldonado@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20950}

test/testsupport/perf_test.h

@@ -8,16 +8,13 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-// A stripped-down version of Chromium's chrome/test/perf/perf_test.h.
-// Several functions have been removed; the prototypes of the remainder have
-// not been changed.
-
 #ifndef TEST_TESTSUPPORT_PERF_TEST_H_
 #define TEST_TESTSUPPORT_PERF_TEST_H_
 
+#include "api/array_view.h"
+
 #include <sstream>
 #include <string>
-#include <vector>
 
 namespace webrtc {
 namespace test {
@@ -53,7 +50,6 @@ void PrintResultMeanAndError(const std::string& measurement,
                              const std::string& units,
                              bool important);
 
-
 // Like PrintResult(), but prints an entire list of results. The |values|
 // will generally be a list of comma-separated numbers. A typical
 // post-processing step might produce plots of their mean and standard
@@ -61,10 +57,17 @@ void PrintResultMeanAndError(const std::string& measurement,
 void PrintResultList(const std::string& measurement,
                      const std::string& modifier,
                      const std::string& trace,
-                     const std::vector<double>& values,
+                     rtc::ArrayView<const double> values,
                      const std::string& units,
                      bool important);
 
+// Get all perf results to date in a JSON format as described in
+// https://github.com/catapult-project/catapult/blob/master/dashboard/docs/data-format.md
+std::string GetPerfResultsJSON();
+
+// You shouldn't use this function. It's only used to test the functions above.
+void ClearPerfResults();
+
 }  // namespace test
 }  // namespace webrtc