Added DCHECK for monotonicTimeToDOMHighResTimeStamp in PerformanceBase

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

 /*
  * 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 57 matching lines @@
   const AtomicString& interfaceName() const override;
 
   virtual PerformanceTiming* timing() const;
 
   virtual void updateLongTaskInstrumentation() {}
 
   // Reduce the resolution to 5µs to prevent timing attacks. See:
   // http://www.w3.org/TR/hr-time-2/#privacy-security
   static double clampTimeResolution(double timeSeconds);
 
+  // monotonicTime needs to be no smaller than timeOrigin.
   static DOMHighResTimeStamp monotonicTimeToDOMHighResTimeStamp(
       double timeOrigin,
       double monotonicTime);
 
   // Translate given platform monotonic time in seconds into a high resolution
   // DOMHighResTimeStamp in milliseconds. The result timestamp is relative to
   // document's time origin and has a time resolution that is safe for
-  // exposing to web.
+  // exposing to web. The monotonic time provided needs to be no smaller than
+  // document's time origin.
   DOMHighResTimeStamp monotonicTimeToDOMHighResTimeStamp(double) const;
   DOMHighResTimeStamp now() const;
 
   double timeOrigin() const { return m_timeOrigin; }
 
   PerformanceEntryVector getEntries() const;
   PerformanceEntryVector getEntriesByType(const String& entryType);
   PerformanceEntryVector getEntriesByName(const String& name,
                                           const String& entryType);
 
@@ skipping 82 matching lines @@
   PerformanceEntryTypeMask m_observerFilterOptions;
   PerformanceObservers m_observers;
   PerformanceObservers m_activeObservers;
   PerformanceObservers m_suspendedObservers;
   Timer<PerformanceBase> m_deliverObservationsTimer;
 };
 
 }  // namespace blink
 
 #endif  // PerformanceBase_h