Add a task_scheduler tracing category which will record an extra event per task.

base/sequence_token_unittest.cc

Index: base/sequence_token_unittest.cc
diff --git a/base/sequence_token_unittest.cc b/base/sequence_token_unittest.cc
index 23e6283e9c2f7cda8f1ad674b62fbab28794bce2..50daa8dd45400c3db5f1f82f326a5dcd368124ba 100644
--- a/base/sequence_token_unittest.cc
+++ b/base/sequence_token_unittest.cc
@@ -4,6 +4,7 @@
 
 #include "base/sequence_token.h"
 
+#include "base/strings/string_number_conversions.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
@@ -62,6 +63,24 @@ TEST(SequenceTokenTest, GetForCurrentThread) {
   EXPECT_FALSE(SequenceToken::GetForCurrentThread().IsValid());
 }
 
+TEST(SequenceTokenTest, ToString) {
+  const SequenceToken token1 = SequenceToken::Create();
+  const SequenceToken token2 = SequenceToken::Create();
+
+  const std::string token1_str = token1.ToString();
+  const std::string token2_str = token2.ToString();
+
+  // Confirm that the strings are numerical representations.
+  int token1_int = -1;
+  int token2_int = -1;
+  EXPECT_TRUE(StringToInt(token1_str, &token1_int));
+  EXPECT_TRUE(StringToInt(token2_str, &token2_int));
+
+  // Confirm that they are unique.
+  EXPECT_NE(token1_str, token2_str);
+  EXPECT_NE(token1_int, token2_int);
+}
+
 // Expect a default-constructed TaskToken to be invalid and not equal to
 // another invalid TaskToken.
 TEST(TaskTokenTest, InvalidDefaultConstructed) {