Introduce a CompilerDispatcherTracer and track how long jobs take

src/base/ring-buffer.h

+// 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.
+
+#ifndef V8_BASE_RING_BUFFER_H_
+#define V8_BASE_RING_BUFFER_H_
+
+#include "src/base/macros.h"
+
+namespace v8 {
+namespace base {
+
+template <typename T>
+class RingBuffer {
+ public:
+  RingBuffer() { Reset(); }
+  static const int kSize = 10;
+  void Push(const T& value) {
+    if (count_ == kSize) {
+      elements_[start_++] = value;
+      if (start_ == kSize) start_ = 0;
+    } else {
+      DCHECK_EQ(start_, 0);
+      elements_[count_++] = value;
+    }
+  }
+
+  int Count() const { return count_; }
+
+  template <typename Callback>
+  T Sum(Callback callback, const T& initial) const {
+    int j = start_ + count_ - 1;
+    if (j >= kSize) j -= kSize;
+    T result = initial;
+    for (int i = 0; i < count_; i++) {
+      result = callback(result, elements_[j]);
+      if (--j == -1) j += kSize;
+    }
+    return result;
+  }
+
+  void Reset() { start_ = count_ = 0; }
+
+ private:
+  T elements_[kSize];
+  int start_;
+  int count_;
+  DISALLOW_COPY_AND_ASSIGN(RingBuffer);
+};
+
+}  // namespace base
+}  // namespace v8
+
+#endif  // V8_BASE_RING_BUFFER_H_