Skip default categories when getting known categories.

base/debug/trace_event_unittest.cc

Index: base/debug/trace_event_unittest.cc
diff --git a/base/debug/trace_event_unittest.cc b/base/debug/trace_event_unittest.cc
index 5fb90407c65df90867fbeff5b563616b47be1a03..4bfd799992c16c3852e3aad04d487cc29e9de4de 100644
--- a/base/debug/trace_event_unittest.cc
+++ b/base/debug/trace_event_unittest.cc
@@ -863,7 +863,8 @@ TEST_F(TraceEventTestFixture, Categories) {
   EXPECT_TRUE(std::find(cats.begin(), cats.end(), "c2") != cats.end());
   EXPECT_TRUE(std::find(cats.begin(), cats.end(), "c3") != cats.end());
   EXPECT_TRUE(std::find(cats.begin(), cats.end(), "c4") != cats.end());
-
+  // Make sure metadata isn't returned.
+  EXPECT_TRUE(std::find(cats.begin(), cats.end(), "__metadata") == cats.end());
   const std::vector<std::string> empty_categories;
   std::vector<std::string> included_categories;
   std::vector<std::string> excluded_categories;