Assert event timestamp to be monotonic and not from future

third_party/WebKit/Source/platform/PlatformEvent.h

Index: third_party/WebKit/Source/platform/PlatformEvent.h
diff --git a/third_party/WebKit/Source/platform/PlatformEvent.h b/third_party/WebKit/Source/platform/PlatformEvent.h
index 9a60dce432236401a5f5594e588413788314120a..c03fd4d2023f996e873bc2d44581878964316e2c 100644
--- a/third_party/WebKit/Source/platform/PlatformEvent.h
+++ b/third_party/WebKit/Source/platform/PlatformEvent.h
@@ -27,6 +27,7 @@
 #define PlatformEvent_h
 
 #include "wtf/Allocator.h"
+#include "wtf/CurrentTime.h"
 #include "wtf/Noncopyable.h"
 
 namespace blink {
@@ -159,6 +160,9 @@ protected:
         , m_modifiers(modifiers)
         , m_timestamp(timestamp)
     {
+        // Verify that timestamp is coming from monotonic clock and not the
+        // wall clock.
+        DCHECK(timestamp <= monotonicallyIncreasingTime());
     }
 
     // Explicit protected destructor so that people don't accidentally