Enable FILTERING_MODE for tracing if event filters were given in config

components/tracing/common/trace_startup.cc

 // Copyright 2017 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 "components/tracing/common/trace_startup.h"
 
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/trace_event/memory_dump_manager.h"
 #include "base/trace_event/trace_log.h"
@@ skipping 20 matching lines @@
   } else if (command_line.HasSwitch(switches::kTraceToConsole)) {
     base::trace_event::TraceConfig trace_config =
         tracing::GetConfigForTraceToConsole();
     LOG(ERROR) << "Start " << switches::kTraceToConsole
                << " with CategoryFilter '"
                << trace_config.ToCategoryFilterString() << "'.";
     base::trace_event::TraceLog::GetInstance()->SetEnabled(
         trace_config, base::trace_event::TraceLog::RECORDING_MODE);
   } else if (can_access_file_system &&
              tracing::TraceConfigFile::GetInstance()->IsEnabled()) {
+    const base::trace_event::TraceConfig& trace_config =
+        tracing::TraceConfigFile::GetInstance()->GetTraceConfig();
+    uint8_t modes = base::trace_event::TraceLog::RECORDING_MODE;
+    if (!trace_config.event_filters().empty())
+      modes |= base::trace_event::TraceLog::FILTERING_MODE;
     // This checks kTraceConfigFile switch.
     base::trace_event::TraceLog::GetInstance()->SetEnabled(
-        tracing::TraceConfigFile::GetInstance()->GetTraceConfig(),
-        base::trace_event::TraceLog::RECORDING_MODE);
+        tracing::TraceConfigFile::GetInstance()->GetTraceConfig(), modes);
   }
 }
 
 }  // namespace tracing