Generate globally (cross-process) unique IDs for memory tracing dumps

base/trace_event/trace_event_impl.cc

Index: base/trace_event/trace_event_impl.cc
diff --git a/base/trace_event/trace_event_impl.cc b/base/trace_event/trace_event_impl.cc
index 834f826e04078dae5b992276b986a1581f6a1037..f312c71dfaed3ad865267dee19ae3275d4dcb0bc 100644
--- a/base/trace_event/trace_event_impl.cc
+++ b/base/trace_event/trace_event_impl.cc
@@ -1921,7 +1921,7 @@ TraceEventHandle TraceLog::AddTraceEventWithThreadIdAndTimestamp(
   DCHECK(!timestamp.is_null());
 
   if (flags & TRACE_EVENT_FLAG_MANGLE_ID)
-    id ^= process_id_hash_;
+    id = MangleEventId(id);
 
   TimeTicks offset_event_timestamp = OffsetTimestamp(timestamp);
   TimeTicks now = flags & TRACE_EVENT_FLAG_EXPLICIT_TIMESTAMP ?
@@ -2190,6 +2190,10 @@ void TraceLog::CancelWatchEvent() {
   watch_event_callback_.Reset();
 }
 
+uint64 TraceLog::MangleEventId(uint64 id) {
+  return id ^ process_id_hash_;
+}
+
 void TraceLog::AddMetadataEventsWhileLocked() {
   lock_.AssertAcquired();