[tracing] Add a DCHECK to ensure that trace events have a valid timestamp.

base/trace_event/trace_event_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/trace_event/trace_event_impl.h"
 
 #include <algorithm>
 
 #include "base/base_switches.h"
 #include "base/bind.h"
@@ skipping 1903 matching lines @@
 
   // Avoid re-entrance of AddTraceEvent. This may happen in GPU process when
   // ECHO_TO_CONSOLE is enabled: AddTraceEvent -> LOG(ERROR) ->
   // GpuProcessLogMessageHandler -> PostPendingTask -> TRACE_EVENT ...
   if (thread_is_in_trace_event_.Get())
     return handle;
 
   AutoThreadLocalBoolean thread_is_in_trace_event(&thread_is_in_trace_event_);
 
   DCHECK(name);
+  DCHECK(!timestamp.is_null());
 
   if (flags & TRACE_EVENT_FLAG_MANGLE_ID)
     id ^= process_id_hash_;
 
   TimeTicks now = OffsetTimestamp(timestamp);
   TimeTicks thread_now = ThreadNow();
 
   ThreadLocalEventBuffer* thread_local_event_buffer = NULL;
   // A ThreadLocalEventBuffer needs the message loop
   // - to know when the thread exits;
@@ skipping 664 matching lines @@
 }
 
 ScopedTraceBinaryEfficient::~ScopedTraceBinaryEfficient() {
   if (*category_group_enabled_) {
     TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(category_group_enabled_,
                                                 name_, event_handle_);
   }
 }
 
 }  // namespace trace_event_internal