Add an explicit way of making IDs local or global

base/trace_event/common/trace_event_common.h

Index: base/trace_event/common/trace_event_common.h
diff --git a/base/trace_event/common/trace_event_common.h b/base/trace_event/common/trace_event_common.h
index 0c16e7b72382d3d56b17df4761798cc6f6bc202a..79470b2d0fa3d18c960dd8e73ae0038838dc26ac 100644
--- a/base/trace_event/common/trace_event_common.h
+++ b/base/trace_event/common/trace_event_common.h
@@ -965,41 +965,40 @@
 // See also TraceTrackableObject.
 #define TRACE_EVENT_OBJECT_CREATED_WITH_ID(category_group, name, id) \
   INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                  \
-      TRACE_EVENT_PHASE_CREATE_OBJECT, category_group, name,         \
-      TRACE_ID_DONT_MANGLE(id), TRACE_EVENT_FLAG_NONE)
+      TRACE_EVENT_PHASE_CREATE_OBJECT, category_group, name, id,     \
+      TRACE_EVENT_FLAG_NONE)
 
 #define TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID(category_group, name, id, \
                                             snapshot)                 \
   INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                   \
       TRACE_EVENT_PHASE_SNAPSHOT_OBJECT, category_group, name,        \
-      TRACE_ID_DONT_MANGLE(id), TRACE_EVENT_FLAG_NONE, "snapshot", snapshot)
+      id, TRACE_EVENT_FLAG_NONE, "snapshot", snapshot)
 
-#define TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID_AND_TIMESTAMP(                    \
-    category_group, name, id, timestamp, snapshot)                            \
-  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                         \
-      TRACE_EVENT_PHASE_SNAPSHOT_OBJECT, category_group, name,                \
-      TRACE_ID_DONT_MANGLE(id), TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, \
-      TRACE_EVENT_FLAG_NONE, "snapshot", snapshot)
+#define TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID_AND_TIMESTAMP(                     \
+    category_group, name, id, timestamp, snapshot)                             \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(                          \
+      TRACE_EVENT_PHASE_SNAPSHOT_OBJECT, category_group, name,                 \
+      id, TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, TRACE_EVENT_FLAG_NONE, \
+      "snapshot", snapshot)
 
 #define TRACE_EVENT_OBJECT_DELETED_WITH_ID(category_group, name, id) \
   INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                  \
-      TRACE_EVENT_PHASE_DELETE_OBJECT, category_group, name,         \
-      TRACE_ID_DONT_MANGLE(id), TRACE_EVENT_FLAG_NONE)
+      TRACE_EVENT_PHASE_DELETE_OBJECT, category_group, name, id,     \
+      TRACE_EVENT_FLAG_NONE)
 
 // Records entering and leaving trace event contexts. |category_group| and
 // |name| specify the context category and type. |context| is a
 // snapshotted context object id.
-#define TRACE_EVENT_ENTER_CONTEXT(category_group, name, context) \
-  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                              \
-      TRACE_EVENT_PHASE_ENTER_CONTEXT, category_group, name,     \
-      TRACE_ID_DONT_MANGLE(context), TRACE_EVENT_FLAG_NONE)
-#define TRACE_EVENT_LEAVE_CONTEXT(category_group, name, context) \
-  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                              \
-      TRACE_EVENT_PHASE_LEAVE_CONTEXT, category_group, name,     \
-      TRACE_ID_DONT_MANGLE(context), TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_ENTER_CONTEXT(category_group, name, context)      \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                   \
+      TRACE_EVENT_PHASE_ENTER_CONTEXT, category_group, name, context, \
+      TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_LEAVE_CONTEXT(category_group, name, context)      \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                                   \
+      TRACE_EVENT_PHASE_LEAVE_CONTEXT, category_group, name, context, \
+      TRACE_EVENT_FLAG_NONE)
 #define TRACE_EVENT_SCOPED_CONTEXT(category_group, name, context) \
-  INTERNAL_TRACE_EVENT_SCOPED_CONTEXT(category_group, name,       \
-                                      TRACE_ID_DONT_MANGLE(context))
+  INTERNAL_TRACE_EVENT_SCOPED_CONTEXT(category_group, name, context)
 
 // Macro to specify that two trace IDs are identical. For example,
 // TRACE_BIND_IDS(
@@ -1083,6 +1082,7 @@
 #define TRACE_EVENT_FLAG_NONE (static_cast<unsigned int>(0))
 #define TRACE_EVENT_FLAG_COPY (static_cast<unsigned int>(1 << 0))
 #define TRACE_EVENT_FLAG_HAS_ID (static_cast<unsigned int>(1 << 1))
+// TODO(crbug.com/639003): Free this bit after ID mangling is deprecated.

[Primiano Tucci (use gerrit), 2016/08/31 19:11:22]

Nononono that would break backwards compat if somebody frees this bit and
somebody else reuses it.
At most this should be just renamed to TRACE_EVENT_FLAG_MANGLE_ID_DEPRECATED.
But probably such rename would have disastrous consequences on other projects
depending on this file, so I'll just say here:
// Deprecated, use HAS_{LOCAL,GLOBAL}_ID below.

[caseq, 2016/08/31 19:17:10]

What backward compat are we talking about here? This is not exposed in the trace
output and is purely an implementation detail of the tracing subsystem. I reckon
we have events from couple of other components, but those should be easy to
update.

 #define TRACE_EVENT_FLAG_MANGLE_ID (static_cast<unsigned int>(1 << 2))
 #define TRACE_EVENT_FLAG_SCOPE_OFFSET (static_cast<unsigned int>(1 << 3))
 #define TRACE_EVENT_FLAG_SCOPE_EXTRA (static_cast<unsigned int>(1 << 4))
@@ -1093,7 +1093,12 @@
 #define TRACE_EVENT_FLAG_FLOW_OUT (static_cast<unsigned int>(1 << 9))
 #define TRACE_EVENT_FLAG_HAS_CONTEXT_ID (static_cast<unsigned int>(1 << 10))
 #define TRACE_EVENT_FLAG_HAS_PROCESS_ID (static_cast<unsigned int>(1 << 11))
+#define TRACE_EVENT_FLAG_HAS_LOCAL_ID (static_cast<unsigned int>(1 << 12))
+#define TRACE_EVENT_FLAG_HAS_GLOBAL_ID (static_cast<unsigned int>(1 << 1 | \

[Primiano Tucci (use gerrit), 2016/08/31 19:11:22]

had a chat offline, saving this one bit is making the sources really hard to
read.
Please just use another bit, the code below trace_event_impl.cc where *almost*
every _FLAG_ (but not GLOBAL_ID) is a bit tripped my mind :)
I deal daily with multi-MB regressions, I can guarantee we can still afford an
extra bit in chrome, nobody will notice :P

[chiniforooshan, 2016/08/31 21:28:45]

Done.

+                                                                  1 << 12))
 
+#define TRACE_EVENT_FLAG_ID_MASK (TRACE_EVENT_FLAG_HAS_LOCAL_ID | \
+                                  TRACE_EVENT_FLAG_HAS_GLOBAL_ID)
 #define TRACE_EVENT_FLAG_SCOPE_MASK                          \
   (static_cast<unsigned int>(TRACE_EVENT_FLAG_SCOPE_OFFSET | \
                              TRACE_EVENT_FLAG_SCOPE_EXTRA))