cc: Avoid posting renewTreePriority tasks with negative delay.

cc/thread_proxy.cc

Index: cc/thread_proxy.cc
diff --git a/cc/thread_proxy.cc b/cc/thread_proxy.cc
index fe92817ea58a659061e98380f4953a1c5dd5043c..45148a33d257ee5cf0c73e7ebf4fd422b56bb44d 100644
--- a/cc/thread_proxy.cc
+++ b/cc/thread_proxy.cc
@@ -1191,16 +1191,16 @@ void ThreadProxy::renewTreePriority()
             priority == SMOOTHNESS_TAKES_PRIORITY);
     }
 
+    base::TimeDelta delay = m_smoothnessTakesPriorityExpirationTime -
+        base::TimeTicks::Now();
+
     // Need to make sure a delayed task is posted when we have smoothness
     // takes priority expiration time in the future.
-    if (m_smoothnessTakesPriorityExpirationTime <= base::TimeTicks::Now())
+    if (delay <= base::TimeDelta())
         return;
     if (m_renewTreePriorityOnImplThreadPending)
         return;
 
-    base::TimeDelta delay = m_smoothnessTakesPriorityExpirationTime -
-        base::TimeTicks::Now();
-
     Proxy::implThread()->postDelayedTask(
         base::Bind(&ThreadProxy::renewTreePriorityOnImplThread,
                    m_weakFactoryOnImplThread.GetWeakPtr()),