Add VMMetric and some sample metrics

runtime/vm/metrics_test.cc

Index: runtime/vm/metrics_test.cc
diff --git a/runtime/vm/metrics_test.cc b/runtime/vm/metrics_test.cc
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+++ b/runtime/vm/metrics_test.cc
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+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#include "platform/assert.h"
+
+#include "vm/dart_api_impl.h"
+#include "vm/dart_api_state.h"
+#include "vm/globals.h"
+#include "vm/json_stream.h"
+#include "vm/metrics.h"
+#include "vm/unit_test.h"
+
+namespace dart {
+
+UNIT_TEST_CASE(Metric_Simple) {
+  Isolate* isolate = Isolate::Init(NULL);
+  EXPECT_EQ(isolate, Isolate::Current());
+  Metric metric;
+
+  // Initialize metric.
+  metric.Init(Isolate::Current(), "a.b.c", "foobar", Metric::kCounter);
+  EXPECT_EQ(0, metric.value());
+  metric.increment();
+  EXPECT_EQ(1, metric.value());
+  metric.set_value(44);
+  EXPECT_EQ(44, metric.value());
+}
+
+class MyMetric : public Metric {
+ protected:
+  int64_t Value() const {
+    // 99 bytes.
+    return 99;
+  }
+
+ public:
+  // Just used for testing.
+  int64_t LeakyValue() const { return Value(); }
+};
+
+UNIT_TEST_CASE(Metric_OnDemand) {
+  Isolate* isolate = Isolate::Init(NULL);
+  EXPECT_EQ(isolate, Isolate::Current());
+  MyMetric metric;
+
+  metric.Init(Isolate::Current(), "a.b.c", "foobar", Metric::kByte);
+  // value is still the default value.
+  EXPECT_EQ(0, metric.value());
+  // Call LeakyValue to confirm that Value returns constant 99.
+  EXPECT_EQ(99, metric.LeakyValue());
+
+  // Serialize to JSON.
+  JSONStream js;
+  metric.PrintJSON(&js);
+  const char* json = js.ToCString();
+  EXPECT_STREQ("{\"type\":\"Counter\",\"name\":\"a.b.c\",\"description\":"
+               "\"foobar\",\"unit\":\"byte\",\"id\":\"metrics\\/vm\\/a.b.c\""
+               ",\"value\":99.000000}", json);
+}
+
+}  // namespace dart