tracing: Introduce API for composite IDs

base/trace_event/trace_event_unittest.cc

Index: base/trace_event/trace_event_unittest.cc
diff --git a/base/trace_event/trace_event_unittest.cc b/base/trace_event/trace_event_unittest.cc
index 81d043ac3945d3582b0a99c22f4adb22d1bd8a21..d72c574dff03b01d786cf89220ba8631a5d80ec0 100644
--- a/base/trace_event/trace_event_unittest.cc
+++ b/base/trace_event/trace_event_unittest.cc
@@ -524,6 +524,8 @@ void TraceWithAllMacroVariants(WaitableEvent* task_complete_event) {
                    TRACE_ID_LOCAL(0x2000));
     TRACE_LINK_IDS("all", "TRACE_LINK_IDS to a global ID", 0x1000,
                    TRACE_ID_GLOBAL(0x2000));
+    TRACE_LINK_IDS("all", "TRACE_LINK_IDS to a composite ID", 0x1000,
+                   TRACE_ID_COMPOSITE(0x2000, 0x3000));
 
     TRACE_EVENT_ASYNC_BEGIN0("all", "async default process scope", 0x1000);
     TRACE_EVENT_ASYNC_BEGIN0("all", "async local id", TRACE_ID_LOCAL(0x2000));
@@ -1044,6 +1046,29 @@ void ValidateAllTraceMacrosCreatedData(const ListValue& trace_parsed) {
     EXPECT_EQ("0x2000", id2);
   }
 
+  EXPECT_FIND_("TRACE_LINK_IDS to a composite ID");
+  {
+    std::string ph;
+    EXPECT_TRUE((item && item->GetString("ph", &ph)));
+    EXPECT_EQ("=", ph);
+
+    EXPECT_FALSE(item->HasKey("scope"));
+    std::string id1;
+    EXPECT_TRUE(item->GetString("id", &id1));
+    EXPECT_EQ("0x1000", id1);
+
+    EXPECT_FALSE(item->HasKey("args.linked_id.scope"));
+    const base::ListValue* id2 = nullptr;
+    EXPECT_TRUE(item->GetList("args.linked_id.id", &id2));
+    EXPECT_EQ(static_cast<size_t>(2), id2->GetSize());
+    std::string part1;
+    EXPECT_TRUE(id2->GetString(0, &part1));
+    EXPECT_EQ("0x2000", part1);
+    std::string part2;
+    EXPECT_TRUE(id2->GetString(1, &part2));
+    EXPECT_EQ("0x3000", part2);
+  }
+
   EXPECT_FIND_("async default process scope");
   {
     std::string ph;