Add Chromium-style TimeDelta, Time and TimeTicks classes, and a new ElapsedTimer class.

src/time/elapsed-timer.h

Index: src/time/elapsed-timer.h
diff --git a/src/time/elapsed-timer.h b/src/time/elapsed-timer.h
new file mode 100644
index 0000000000000000000000000000000000000000..02e28e89f76da4da035b80265f5acc3a63012e4c
--- /dev/null
+++ b/src/time/elapsed-timer.h
@@ -0,0 +1,120 @@
+// Copyright 2013 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef V8_TIME_ELAPSED_TIMER_H_
+#define V8_TIME_ELAPSED_TIMER_H_
+
+#include "checks.h"
+#include "time/time.h"
+
+namespace v8 {
+namespace internal {
+
+class ElapsedTimer V8_FINAL BASE_EMBEDDED {
+ public:
+#ifdef DEBUG
+  ElapsedTimer() : started_(false) {}
+#endif
+
+  // Starts this timer. Once started a timer can be checked with
+  // |Elapsed()| or |HasExpired()|, and may be restarted using |Restart()|.
+  // This method must not be called on an already started timer.
+  void Start() {
+    ASSERT(!IsStarted());
+    start_ticks_ = Now();
+#ifdef DEBUG
+    started_ = true;
+#endif
+    ASSERT(IsStarted());
+  }
+
+  // Stops this timer. Must not be called on a timer that was not
+  // started before.
+  void Stop() {
+    ASSERT(IsStarted());
+    start_ticks_ = TimeTicks();
+#ifdef DEBUG
+    started_ = false;
+#endif
+    ASSERT(!IsStarted());
+  }
+
+  // Returns |true| if this timer was started previously.
+  bool IsStarted() const {
+    ASSERT(started_ || start_ticks_.IsNull());
+    ASSERT(!started_ || !start_ticks_.IsNull());
+    return !start_ticks_.IsNull();
+  }
+
+  // Restarts the timer and returns the time elapsed since the previous start.
+  // This method is equivalent to obtaining the elapsed time with |Elapsed()|
+  // and then starting the timer again, but does so in one single operation,
+  // avoiding the need to obtain the clock value twice. It may only be called
+  // on a previously started timer.
+  TimeDelta Restart() {
+    ASSERT(IsStarted());

[tfarina, 2013/09/07 04:15:40]

why all the implementations are in the header file? does that brings any
advantage over declaring in the header and implementing in the source file? if
yes, how did you measure it?

[Benedikt Meurer, 2013/09/09 05:55:18]

The implementation is trivial, one method invocation and one subtraction
(inlined from TimeTicks - operator). We usually just inline stuff like this in
the header.

+    TimeTicks ticks = Now();
+    TimeDelta elapsed = ticks - start_ticks_;
+    ASSERT(elapsed.InMicroseconds() >= 0);
+    start_ticks_ = ticks;
+    ASSERT(IsStarted());
+    return elapsed;
+  }
+
+  // Returns the time elapsed since the previous start. This method may only
+  // be called on a previously started timer.
+  MUST_USE_RESULT TimeDelta Elapsed() const {
+    ASSERT(IsStarted());
+    TimeDelta elapsed = Now() - start_ticks_;
+    ASSERT(elapsed.InMicroseconds() >= 0);
+    return elapsed;
+  }
+
+  // Returns |true| if the specified |time_delta| has elapsed since the
+  // previous start, or |false| if not. This method may only be called on
+  // a previously started timer.
+  MUST_USE_RESULT bool HasExpired(TimeDelta time_delta) const {
+    ASSERT(IsStarted());
+    return Elapsed() >= time_delta;
+  }
+
+ private:
+  MUST_USE_RESULT V8_INLINE(static TimeTicks Now()) {
+    TimeTicks now = TimeTicks::HighResNow();
+    ASSERT(!now.IsNull());
+    return now;
+  }
+
+  TimeTicks start_ticks_;
+#ifdef DEBUG
+  bool started_;
+#endif
+};
+
+} }  // namespace v8::internal
+
+#endif  // V8_TIME_ELAPSED_TIMER_H_