cc: Add trace events for the Scheduler states.

With upcoming scheduler changes, it'll be easier to understand the
scheduler if there's a tracing option for the scheduler state.

Given how much state there is to trace, a new disabled-by-default
tracing category is used called "cc.debug.scheduler".

BUG=276637

Review URL: https://chromiumcodereview.appspot.com/22802018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@218686 0039d316-1c4b-4281-b951-d872f2087c98

diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index 010cc99..0cf594f 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc

@@ -7,6 +7,7 @@
 #include "base/auto_reset.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
+#include "cc/debug/traced_value.h"
 
 namespace cc {
 
@@ -199,8 +200,13 @@
 
   base::AutoReset<bool> mark_inside(&inside_process_scheduled_actions_, true);
 
-  SchedulerStateMachine::Action action = state_machine_.NextAction();
-  while (action != SchedulerStateMachine::ACTION_NONE) {
+  SchedulerStateMachine::Action action;
+  do {
+    action = state_machine_.NextAction();
+    TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("cc.debug.scheduler"),
+                 "SchedulerStateMachine",
+                 "state",
+                 TracedValue::FromValue(state_machine_.AsValue().release()));
     state_machine_.UpdateState(action);
     switch (action) {
       case SchedulerStateMachine::ACTION_NONE:
@@ -230,8 +236,7 @@
         client_->ScheduledActionAcquireLayerTexturesForMainThread();
         break;
     }
-    action = state_machine_.NextAction();
-  }
+  } while (action != SchedulerStateMachine::ACTION_NONE);
 
   SetupNextBeginFrameIfNeeded();
   client_->DidAnticipatedDrawTimeChange(AnticipatedDrawTime());