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

components/tracing/child_trace_message_filter.cc

Index: components/tracing/child_trace_message_filter.cc
diff --git a/components/tracing/child_trace_message_filter.cc b/components/tracing/child_trace_message_filter.cc
index ad34a24c352cd6105797c8914977c79451ab50d1..7da7c09887ea0b194ee7ee1171aef65e0b956cc1 100644
--- a/components/tracing/child_trace_message_filter.cc
+++ b/components/tracing/child_trace_message_filter.cc
@@ -4,6 +4,7 @@
 
 #include "components/tracing/child_trace_message_filter.h"
 
+#include "base/trace_event/memory_allocator_dump_guid.h"
 #include "base/trace_event/trace_event.h"
 #include "components/tracing/child_memory_dump_manager_delegate_impl.h"
 #include "components/tracing/tracing_messages.h"
@@ -58,7 +59,8 @@ ChildTraceMessageFilter::~ChildTraceMessageFilter() {}
 
 void ChildTraceMessageFilter::OnBeginTracing(
     const std::string& trace_config_str,
-    base::TraceTicks browser_time) {
+    base::TraceTicks browser_time,
+    int child_process_id) {
 #if defined(__native_client__)
   // NaCl and system times are offset by a bit, so subtract some time from
   // the captured timestamps. The value might be off by a bit due to messaging
@@ -66,6 +68,8 @@ void ChildTraceMessageFilter::OnBeginTracing(
   base::TimeDelta time_offset = base::TraceTicks::Now() - browser_time;
   TraceLog::GetInstance()->SetTimeOffset(time_offset);
 #endif
+  base::trace_event::MemoryAllocatorDumpGuid::SetUniqueChildProcessId(

[Primiano Tucci (use gerrit), 2015/06/19 13:47:50]

Can you also clear this at OnEndTracing below?

[ssid, 2015/06/19 14:51:19]

Done.

+      child_process_id);
   TraceLog::GetInstance()->SetEnabled(
       base::trace_event::TraceConfig(trace_config_str),
       base::trace_event::TraceLog::RECORDING_MODE);