Introduce a CompilerDispatcherTracer and track how long jobs take

test/unittests/compiler-dispatcher/compiler-dispatcher-tracer-unittest.cc

+// Copyright 2016 the V8 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.
+
+#include "src/compiler-dispatcher/compiler-dispatcher-tracer.h"
+#include "testing/gtest-support.h"
+
+namespace v8 {
+namespace internal {
+
+TEST(CompilerDispatcherTracerTest, EstimateZeroWithoutSamples) {
+  CompilerDispatcherTracer tracer(nullptr);
+
+  EXPECT_EQ(0.0, tracer.EstimatePrepareToParse());
+  EXPECT_EQ(0.0, tracer.EstimateParse(0));
+  EXPECT_EQ(0.0, tracer.EstimateParse(42));
+  EXPECT_EQ(0.0, tracer.EstimateFinalizeParsing());
+  EXPECT_EQ(0.0, tracer.EstimatePrepareToCompile());
+  EXPECT_EQ(0.0, tracer.EstimateCompile(0));
+  EXPECT_EQ(0.0, tracer.EstimateCompile(42));
+  EXPECT_EQ(0.0, tracer.EstimateFinalizeCompiling());
+}
+
+TEST(CompilerDispatcherTracerTest, Average) {
+  CompilerDispatcherTracer tracer(nullptr);
+
+  EXPECT_EQ(0.0, tracer.EstimatePrepareToParse());
+
+  tracer.RecordPrepareToParse(1.0);
+  tracer.RecordPrepareToParse(2.0);
+  tracer.RecordPrepareToParse(3.0);
+
+  EXPECT_EQ((1.0 + 2.0 + 3.0) / 3, tracer.EstimatePrepareToParse());
+}
+
+TEST(CompilerDispatcherTracerTest, SizeBasedAverage) {
+  CompilerDispatcherTracer tracer(nullptr);
+
+  EXPECT_EQ(0.0, tracer.EstimatePrepareToParse());
+
+  // All three samples parse 100 units/ms.
+  tracer.RecordParse(1.0, 100);
+  tracer.RecordParse(2.0, 200);
+  tracer.RecordParse(3.0, 300);
+
+  EXPECT_EQ(1.0, tracer.EstimateParse(100));
+  EXPECT_EQ(5.0, tracer.EstimateParse(500));
+}
+
+}  // namespace internal
+}  // namespace v8