Added DCHECK for monotonicTimeToDOMHighResTimeStamp in PerformanceBase

third_party/WebKit/Source/core/timing/PerformanceBase.cpp

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2012 Intel Inc. 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.
@@ skipping 551 matching lines @@
       observer->deliver();
   }
 }
 
 // static
 double PerformanceBase::clampTimeResolution(double timeSeconds) {
   const double resolutionSeconds = 0.000005;
   return floor(timeSeconds / resolutionSeconds) * resolutionSeconds;
 }
 
 DOMHighResTimeStamp PerformanceBase::monotonicTimeToDOMHighResTimeStamp(

[skobes, 2017/01/13 22:31:44]

I suggest adding a comment to the declaration of this public function in the
header file, documenting the new precondition that monotonicTime > timeOrigin.

Have you audited the existing callers to ensure that none of them violate this?

[sunjian, 2017/01/14 01:04:32]

Done. I don't think anyone else violates the DCHECK except for the tests we
modified in this patch.

     double timeOrigin,
     double monotonicTime) {
   // Avoid exposing raw platform timestamps.
   if (!monotonicTime || !timeOrigin)
     return 0.0;
 
   double timeInSeconds = monotonicTime - timeOrigin;
-  if (timeInSeconds < 0)
-    return 0.0;
+  DCHECK_GE(timeInSeconds, 0);
   return convertSecondsToDOMHighResTimeStamp(
       clampTimeResolution(timeInSeconds));
 }
 
 DOMHighResTimeStamp PerformanceBase::monotonicTimeToDOMHighResTimeStamp(
     double monotonicTime) const {
   return monotonicTimeToDOMHighResTimeStamp(m_timeOrigin, monotonicTime);
 }
 
 DOMHighResTimeStamp PerformanceBase::now() const {
   return monotonicTimeToDOMHighResTimeStamp(monotonicallyIncreasingTime());
 }
 
 DEFINE_TRACE(PerformanceBase) {
   visitor->trace(m_frameTimingBuffer);
   visitor->trace(m_resourceTimingBuffer);
   visitor->trace(m_navigationTiming);
   visitor->trace(m_userTiming);
   visitor->trace(m_observers);
   visitor->trace(m_activeObservers);
   visitor->trace(m_suspendedObservers);
   EventTargetWithInlineData::trace(visitor);
 }
 
 }  // namespace blink