[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..b685ef1d48ed7b3333afc05a0b8c90604da7777f 100644
--- a/content/browser/tracing/trace_message_filter.cc
+++ b/content/browser/tracing/trace_message_filter.cc
@@ -4,14 +4,17 @@
 
 #include "content/browser/tracing/trace_message_filter.h"
 
+#include "base/hash.h"
+#include "base/strings/string_number_conversions.h"
 #include "components/tracing/tracing_messages.h"
 #include "content/browser/tracing/tracing_controller_impl.h"
 
 namespace content {
 
-TraceMessageFilter::TraceMessageFilter()
+TraceMessageFilter::TraceMessageFilter(int child_process_id)
     : BrowserMessageFilter(TracingMsgStart),
       has_child_(false),
+      tracing_process_id_(base::Hash(base::IntToString(child_process_id))),

[Primiano Tucci (use gerrit), 2015/06/23 13:35:20]

This should be a method of MDM. Otherwise there is no way for the browser-side
dumpers to construct a corresponding string.
Also add a comment explaining why we are hashing and a pointer to the discussion
and design doc.

Introduce a public static int
MemoryDumpManager::ChildProcessIdToTracingProcessId(int child_process_id)
method.

[ssid, 2015/06/24 08:37:57]

Done.

       is_awaiting_end_ack_(false),
       is_awaiting_capture_monitoring_snapshot_ack_(false),
       is_awaiting_buffer_percent_full_ack_(false) {
@@ -63,8 +66,8 @@ bool TraceMessageFilter::OnMessageReceived(const IPC::Message& message) {
 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()));
+  Send(new TracingMsg_BeginTracing(
+      trace_config.ToString(), base::TraceTicks::Now(), tracing_process_id_));
 }
 
 void TraceMessageFilter::SendEndTracing() {