Add process uptime metadata event in tracing

base/trace_event/trace_log.cc

Index: base/trace_event/trace_log.cc
diff --git a/base/trace_event/trace_log.cc b/base/trace_event/trace_log.cc
index 6dddb94018f6e1b6ec0047f22460c2940399b076..4c03aeb0585d04dba86c9a2fa528a9f555eafcc5 100644
--- a/base/trace_event/trace_log.cc
+++ b/base/trace_event/trace_log.cc
@@ -19,6 +19,7 @@
 #include "base/memory/ref_counted_memory.h"
 #include "base/memory/singleton.h"
 #include "base/message_loop/message_loop.h"
+#include "base/process/process_info.h"
 #include "base/process/process_metrics.h"
 #include "base/stl_util.h"
 #include "base/strings/string_split.h"
@@ -1500,6 +1501,16 @@ void TraceLog::AddMetadataEventsWhileLocked() {
                             process_name_);
   }
 
+#if !defined(OS_NACL) && !defined(OS_IOS)
+  Time process_creation_time = CurrentProcessInfo::CreationTime();
+  if (!process_creation_time.is_null()) {
+    TimeDelta process_uptime = Time::Now() - process_creation_time;
+    InitializeMetadataEvent(AddEventToThreadSharedChunkWhileLocked(NULL, false),
+                            current_thread_id, "process_uptime_seconds",
+                            "uptime", process_uptime.InSeconds());
+  }
+#endif  // !defined(OS_NACL) && !defined(OS_IOS)
+
   if (!process_labels_.empty()) {
     std::vector<std::string> labels;
     for (const auto& it : process_labels_)