[wpilibc] Add ScopedTracer class (#2724)

This makes it easier for C++ teams to log a certain piece of code using RAII.

wpilibc/src/test/native/cpp/ScopedTracerTest.cpp

@@ -0,0 +1,33 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2020 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include <string>
+#include <thread>
+
+#include <wpi/SmallString.h>
+#include <wpi/StringRef.h>
+#include <wpi/raw_ostream.h>
+
+#include "frc/ScopedTracer.h"
+#include "gtest/gtest.h"
+
+wpi::SmallString<128> buf;
+wpi::raw_svector_ostream os(buf);
+
+#ifdef __APPLE__
+TEST(ScopedTracerTest, DISABLED_Timing) {
+#else
+TEST(ScopedTracerTest, Timing) {
+#endif
+  {
+    frc::ScopedTracer tracer("timing_test", os);
+    std::this_thread::sleep_for(std::chrono::milliseconds(1500));
+  }
+
+  wpi::StringRef out = os.str();
+  EXPECT_TRUE(out.startswith("	timing_test: 1.5"));
+}