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

cc/trees/thread_proxy.cc

Index: cc/trees/thread_proxy.cc
diff --git a/cc/trees/thread_proxy.cc b/cc/trees/thread_proxy.cc
index 264c11f098a84248ce2cf74a7482083fddd9f478..f217d017a1c007eeefe6f4592a14fc0eb087a734 100644
--- a/cc/trees/thread_proxy.cc
+++ b/cc/trees/thread_proxy.cc
@@ -824,7 +824,7 @@ void ThreadProxy::ScheduledActionCommit() {
       layer_tree_host_->BlocksPendingCommit()) {
     // 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);
     completion_event_for_commit_held_on_tree_activation_ =
         commit_completion_event_on_impl_thread_;
     commit_completion_event_on_impl_thread_ = NULL;
@@ -910,7 +910,8 @@ ThreadProxy::ScheduledActionDrawAndSwapInternal(bool forced_draw) {
   // Check for tree activation.
   if (completion_event_for_commit_held_on_tree_activation_ &&
       !layer_tree_host_impl_->pending_tree()) {
-    TRACE_EVENT_INSTANT0("cc", "ReleaseCommitbyActivation");
+    TRACE_EVENT_INSTANT0("cc", "ReleaseCommitbyActivation",
+                         TRACE_EVENT_SCOPE_THREAD);
     DCHECK(layer_tree_host_impl_->settings().impl_side_painting);
     completion_event_for_commit_held_on_tree_activation_->Signal();
     completion_event_for_commit_held_on_tree_activation_ = NULL;