Added DCHECK for monotonicTimeToDOMHighResTimeStamp in PerformanceBase

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

Index: third_party/WebKit/Source/core/timing/PerformanceBase.h
diff --git a/third_party/WebKit/Source/core/timing/PerformanceBase.h b/third_party/WebKit/Source/core/timing/PerformanceBase.h
index db35f6c80f5bdbde1d9e5f6573bcede630522ac5..d4d9f6971731754c9130e8477dfeb8f1ae7594d0 100644
--- a/third_party/WebKit/Source/core/timing/PerformanceBase.h
+++ b/third_party/WebKit/Source/core/timing/PerformanceBase.h
@@ -75,6 +75,7 @@ class CORE_EXPORT PerformanceBase : public EventTargetWithInlineData {
   // 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);
@@ -82,7 +83,8 @@ class CORE_EXPORT PerformanceBase : public EventTargetWithInlineData {
   // 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;