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 72b46f92914c8d73d51068324f6c2a757371b5d1..842b608d9ca2d613fad9d4c0019ee02c41e7e5c8 100644
--- a/base/trace_event/trace_event_impl.cc
+++ b/base/trace_event/trace_event_impl.cc
@@ -1908,7 +1908,7 @@ TraceEventHandle TraceLog::AddTraceEventWithThreadIdAndTimestamp(
   DCHECK(!timestamp.is_null());
 
   if (flags & TRACE_EVENT_FLAG_MANGLE_ID)
-    id ^= process_id_hash_;
+    id = HashEventId(id);
 
   TimeTicks offset_event_timestamp = OffsetTimestamp(timestamp);
   TimeTicks now = flags & TRACE_EVENT_FLAG_EXPLICIT_TIMESTAMP ?
@@ -2177,6 +2177,11 @@ void TraceLog::CancelWatchEvent() {
   watch_event_callback_.Reset();
 }
 
+uint64 TraceLog::HashEventId(uint64 id) {
+  return id ^ process_id_hash_;
+}
+
+
 void TraceLog::AddMetadataEventsWhileLocked() {
   lock_.AssertAcquired();