Add a |scope| argument to TRACE_EVENT_INSTANT* and require its presence.

cc/thread_proxy.cc

Index: cc/thread_proxy.cc
diff --git a/cc/thread_proxy.cc b/cc/thread_proxy.cc
index ddc61c07dad0ff2748ad506c0eb6b91a5012acb7..c988a4d978f204d480c684692306d1618c4902f7 100644
--- a/cc/thread_proxy.cc
+++ b/cc/thread_proxy.cc
@@ -760,7 +760,7 @@ void ThreadProxy::scheduledActionCommit()
     {
         // For some layer types in impl-side painting, the commit is held until
         // the pending tree is activated.
-        TRACE_EVENT_INSTANT0("cc", "HoldCommit");
+        TRACE_EVENT_INSTANT0("cc", "HoldCommit", TRACE_EVENT_SCOPE_THREAD);
         m_completionEventForCommitHeldOnTreeActivation = m_commitCompletionEventOnImplThread;
         m_commitCompletionEventOnImplThread = 0;
     }
@@ -842,7 +842,8 @@ ScheduledActionDrawAndSwapResult ThreadProxy::scheduledActionDrawAndSwapInternal
     // Check for tree activation.
     if (m_completionEventForCommitHeldOnTreeActivation && !m_layerTreeHostImpl->pendingTree())
     {
-        TRACE_EVENT_INSTANT0("cc", "ReleaseCommitbyActivation");
+        TRACE_EVENT_INSTANT0("cc", "ReleaseCommitbyActivation",
+                             TRACE_EVENT_SCOPE_THREAD);
         DCHECK(m_layerTreeHostImpl->settings().implSidePainting);
         m_completionEventForCommitHeldOnTreeActivation->signal();
         m_completionEventForCommitHeldOnTreeActivation = 0;