Add builders for tracing event's structural arguments

cc/scheduler/scheduler_state_machine_unittest.cc

Index: cc/scheduler/scheduler_state_machine_unittest.cc
diff --git a/cc/scheduler/scheduler_state_machine_unittest.cc b/cc/scheduler/scheduler_state_machine_unittest.cc
index c89da2f70d1460aba50c0a5629c19b7589aa4c5c..fb51c6bec526977c31cebc3335891f65e5b81071 100644
--- a/cc/scheduler/scheduler_state_machine_unittest.cc
+++ b/cc/scheduler/scheduler_state_machine_unittest.cc
@@ -4,17 +4,18 @@
 
 #include "cc/scheduler/scheduler_state_machine.h"
 
+#include "base/debug/trace_event.h"
 #include "cc/scheduler/scheduler.h"
 #include "cc/test/begin_frame_args_test.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 #define EXPECT_ACTION_UPDATE_STATE(action)                                   \
-  EXPECT_EQ(action, state.NextAction()) << *state.AsValue();                 \
+  EXPECT_EQ(action, state.NextAction()) << state.AsValue()->ToString();      \
   if (action == SchedulerStateMachine::ACTION_DRAW_AND_SWAP_IF_POSSIBLE ||   \
       action == SchedulerStateMachine::ACTION_DRAW_AND_SWAP_FORCED) {        \
     EXPECT_EQ(SchedulerStateMachine::BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE, \
               state.begin_impl_frame_state())                                \
-        << *state.AsValue();                                                 \
+        << state.AsValue()->ToString();                                      \
   }                                                                          \
   state.UpdateState(action);                                                 \
   if (action == SchedulerStateMachine::ACTION_NONE) {                        \