Implement a new flow event API that allows binding flow events and regular events.

ppapi/shared_impl/ppb_trace_event_impl.cc

Index: ppapi/shared_impl/ppb_trace_event_impl.cc
diff --git a/ppapi/shared_impl/ppb_trace_event_impl.cc b/ppapi/shared_impl/ppb_trace_event_impl.cc
index aabc4f255467f5da49147e8efa5efff077f4cbe8..5e5bbb00732c800b421d8eb7d9434edd6b66ae18 100644
--- a/ppapi/shared_impl/ppb_trace_event_impl.cc
+++ b/ppapi/shared_impl/ppb_trace_event_impl.cc
@@ -88,9 +88,9 @@ void TraceEventImpl::AddTraceEventWithThreadIdAndTimestamp(
       // an unsigned long int, but trace_event internals are hermetic and
       // accepts an |unsigned long long*|.  The pointer types are compatible but
       // the compiler throws an error without an explicit cast.
-      reinterpret_cast<const unsigned long long*>(arg_values),
-      NULL,
-      flags);
+          reinterpret_cast<const unsigned long long*>(arg_values),
+          nullptr,
+          flags);
 }
 
 // static