Add a ConvertableToTraceFormat type to the trace framework.

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 8376660300d2d0bc2a9dc8bb0934e178021c93f7..9a7d93ec84538b85265e22a7e2a35643eae607e2 100644
--- a/base/debug/trace_event_unittest.cc
+++ b/base/debug/trace_event_unittest.cc
@@ -1590,6 +1590,46 @@ TEST_F(TraceEventTestFixture, TraceSampling) {
   EXPECT_TRUE(FindNamePhase("Things", "P"));
 }
 
+class MyData : public base::debug::ConvertableToJSON {
+ public:
+  MyData() {}
+  virtual ~MyData() {}
+
+  virtual void ToJSON(std::string& out) const OVERRIDE {
+    out.append("{\"foo\":1}");
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MyData);
+};
+
+TEST_F(TraceEventTestFixture, ConvertableTypes) {
+  ManualTestSetUp();
+  TraceLog::GetInstance()->SetEnabled(true, TraceLog::RECORD_UNTIL_FULL);
+
+  MyData* data(new MyData());
+
+  TRACE_EVENT1("foo", "bar", "data", static_cast<ConvertableToJSON*>(data));
+  EndTraceAndFlush();
+
+  DictionaryValue* dict = FindNamePhase("bar", "B");
+  ASSERT_TRUE(dict);
+
+  const DictionaryValue* args_dict = NULL;
+  dict->GetDictionary("args", &args_dict);
+  ASSERT_TRUE(args_dict);
+
+  const Value* value = NULL;
+  const DictionaryValue* convertable_dict = NULL;
+  EXPECT_TRUE(args_dict->Get("data", &value));
+  EXPECT_TRUE(value->GetAsDictionary(&convertable_dict));
+
+  int foo_val;
+  EXPECT_TRUE(convertable_dict->GetInteger("foo", &foo_val));
+  EXPECT_EQ(1, foo_val);
+}
+
+
 class TraceEventCallbackTest : public TraceEventTestFixture {
  public:
   virtual void SetUp() OVERRIDE {