Enable FILTERING_MODE for tracing if event filters were given in config

components/tracing/child/child_trace_message_filter.cc

Index: components/tracing/child/child_trace_message_filter.cc
diff --git a/components/tracing/child/child_trace_message_filter.cc b/components/tracing/child/child_trace_message_filter.cc
index ed2be875c7da066e73b97ee3e044e14f61b5c68d..2f17f929a423cb26c16e2948e1a97b8b3831b8f6 100644
--- a/components/tracing/child/child_trace_message_filter.cc
+++ b/components/tracing/child/child_trace_message_filter.cc
@@ -25,10 +25,10 @@ const int kMinTimeBetweenHistogramChangesInSeconds = 10;
 
 ChildTraceMessageFilter::ChildTraceMessageFilter(
     base::SingleThreadTaskRunner* ipc_task_runner)
-    : sender_(NULL),
+    : enabled_tracing_modes_(0),
+      sender_(NULL),
       ipc_task_runner_(ipc_task_runner),
-      pending_memory_dump_guid_(0) {
-}
+      pending_memory_dump_guid_(0) {}
 
 void ChildTraceMessageFilter::OnFilterAdded(IPC::Channel* channel) {
   sender_ = channel;
@@ -80,13 +80,17 @@ void ChildTraceMessageFilter::OnBeginTracing(
 #endif
   ChildMemoryDumpManagerDelegateImpl::GetInstance()->set_tracing_process_id(
       tracing_process_id);
-  TraceLog::GetInstance()->SetEnabled(
-      base::trace_event::TraceConfig(trace_config_str),
-      base::trace_event::TraceLog::RECORDING_MODE);
+  const base::trace_event::TraceConfig trace_config(trace_config_str);
+  enabled_tracing_modes_ = base::trace_event::TraceLog::RECORDING_MODE;
+  if (!trace_config.event_filters().empty())
+    enabled_tracing_modes_ |= base::trace_event::TraceLog::FILTERING_MODE;
+  TraceLog::GetInstance()->SetEnabled(trace_config, enabled_tracing_modes_);
 }
 
 void ChildTraceMessageFilter::OnEndTracing() {
-  TraceLog::GetInstance()->SetDisabled();
+  DCHECK(enabled_tracing_modes_);
+  TraceLog::GetInstance()->SetDisabled(enabled_tracing_modes_);
+  enabled_tracing_modes_ = 0;
 
   // Flush will generate one or more callbacks to OnTraceDataCollected
   // synchronously or asynchronously. EndTracingAck will be sent in the last