tracing: Introduce API for composite IDs

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 f9792d0d6df6aea004447b3bf2a293f50d08e646..1f4e0d6699e2c4e52b7d8e89669c57d7c816ae27 100644
--- a/base/trace_event/trace_event_impl.cc
+++ b/base/trace_event/trace_event_impl.cc
@@ -458,30 +458,34 @@ TraceID::AsConvertableToTraceFormat() const {
 
   if (scope_ != kGlobalScope)
     value->SetString("scope", scope_);
-  switch (id_flags_) {
-    case TRACE_EVENT_FLAG_HAS_ID:
-      value->SetString(
-          "id",
-          base::StringPrintf("0x%" PRIx64, static_cast<uint64_t>(raw_id_)));
-      break;
-    case TRACE_EVENT_FLAG_HAS_GLOBAL_ID:
-      value->BeginDictionary("id2");
-      value->SetString(
-          "global",
-          base::StringPrintf("0x%" PRIx64, static_cast<uint64_t>(raw_id_)));
-      value->EndDictionary();
-      break;
-    case TRACE_EVENT_FLAG_HAS_LOCAL_ID:
-      value->BeginDictionary("id2");
-      value->SetString(
-          "local",
-          base::StringPrintf("0x%" PRIx64, static_cast<uint64_t>(raw_id_)));
-      value->EndDictionary();
-      break;
-    default:
-      NOTREACHED() << "Unrecognized ID flag";
+
+  std::string id_field_name = "id";

[caseq, 2016/11/21 19:47:20]

looks like this could be const char* instead.

[chiniforooshan, 2016/11/21 21:12:15]

Done.

+  if (id_flags_ == TRACE_EVENT_FLAG_HAS_GLOBAL_ID) {
+    id_field_name = "global";
+    value->BeginDictionary("id2");
+  } else if (id_flags_ == TRACE_EVENT_FLAG_HAS_LOCAL_ID) {
+    id_field_name = "local";
+    value->BeginDictionary("id2");
+  } else if (id_flags_ != TRACE_EVENT_FLAG_HAS_ID) {
+    NOTREACHED() << "Unrecognized ID flag";
   }
 
+  if (has_prefix_) {
+    value->BeginArrayWithCopiedName(id_field_name);

[caseq, 2016/11/21 19:47:20]

... using const char* would let us get rid of coping here.

[chiniforooshan, 2016/11/21 21:12:15]

Done.

+    value->AppendString(
+        base::StringPrintf("0x%" PRIx64, static_cast<uint64_t>(prefix_)));
+    value->AppendString(
+        base::StringPrintf("0x%" PRIx64, static_cast<uint64_t>(raw_id_)));
+    value->EndArray();
+  } else {
+    value->SetStringWithCopiedName(
+        id_field_name,
+        base::StringPrintf("0x%" PRIx64, static_cast<uint64_t>(raw_id_)));
+  }
+
+  if (id_flags_ != TRACE_EVENT_FLAG_HAS_ID)
+    value->EndDictionary();
+
   return std::move(value);
 }