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

src/platform/elapsed-timer.h

Index: src/platform/elapsed-timer.h
diff --git a/src/platform/elapsed-timer.h b/src/platform/elapsed-timer.h
new file mode 100644
index 0000000000000000000000000000000000000000..e5bcf232f384348258eec5c7a239ce3ec148b007
--- /dev/null
+++ b/src/platform/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_PLATFORM_ELAPSED_TIMER_H_
+#define V8_PLATFORM_ELAPSED_TIMER_H_
+
+#include "checks.h"
+#include "platform/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());
+    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_PLATFORM_ELAPSED_TIMER_H_