[tracing] Send unique tracing process id for cross-process memory dumps identification.

content/browser/tracing/trace_message_filter.cc

Index: content/browser/tracing/trace_message_filter.cc
diff --git a/content/browser/tracing/trace_message_filter.cc b/content/browser/tracing/trace_message_filter.cc
index 1ded8e5fec3efdb75ac9f28d0ab9b8e310eb3006..b7808a44c2c03f6bf58fd98e8077f87f518ba5dc 100644
--- a/content/browser/tracing/trace_message_filter.cc
+++ b/content/browser/tracing/trace_message_filter.cc
@@ -9,9 +9,10 @@
 
 namespace content {
 
-TraceMessageFilter::TraceMessageFilter()
+TraceMessageFilter::TraceMessageFilter(int child_process_id)
     : BrowserMessageFilter(TracingMsgStart),
       has_child_(false),
+      child_process_id_(child_process_id),
       is_awaiting_end_ack_(false),
       is_awaiting_capture_monitoring_snapshot_ack_(false),
       is_awaiting_buffer_percent_full_ack_(false) {
@@ -64,7 +65,7 @@ void TraceMessageFilter::SendBeginTracing(
       const base::trace_event::TraceConfig& trace_config) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   Send(new TracingMsg_BeginTracing(trace_config.ToString(),
-                                   base::TraceTicks::Now()));
+                                   base::TraceTicks::Now(), child_process_id_));
 }
 
 void TraceMessageFilter::SendEndTracing() {