Add support for enabling DCHECKs in release mode

src/base/platform/elapsed-timer.h

 // Copyright 2013 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_PLATFORM_ELAPSED_TIMER_H_
 #define V8_BASE_PLATFORM_ELAPSED_TIMER_H_
 
 #include "src/base/logging.h"
 #include "src/base/platform/time.h"
 
 namespace v8 {
 namespace base {
 
 class ElapsedTimer FINAL {
  public:
-#ifdef DEBUG
+#if DCHECK_IS_ON
   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() {
     DCHECK(!IsStarted());
     start_ticks_ = Now();
-#ifdef DEBUG
+#if DCHECK_IS_ON
     started_ = true;
 #endif
     DCHECK(IsStarted());
   }
 
   // Stops this timer. Must not be called on a timer that was not
   // started before.
   void Stop() {
     DCHECK(IsStarted());
     start_ticks_ = TimeTicks();
-#ifdef DEBUG
+#if DCHECK_IS_ON
     started_ = false;
 #endif
     DCHECK(!IsStarted());
   }
 
   // Returns |true| if this timer was started previously.
   bool IsStarted() const {
     DCHECK(started_ || start_ticks_.IsNull());
     DCHECK(!started_ || !start_ticks_.IsNull());
     return !start_ticks_.IsNull();
@@ skipping 32 matching lines @@
   }
 
  private:
   static V8_INLINE TimeTicks Now() {
     TimeTicks now = TimeTicks::HighResolutionNow();
     DCHECK(!now.IsNull());
     return now;
   }
 
   TimeTicks start_ticks_;
-#ifdef DEBUG
+#if DCHECK_IS_ON
   bool started_;
 #endif
 };
 
 } }  // namespace v8::base
 
 #endif  // V8_BASE_PLATFORM_ELAPSED_TIMER_H_