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

cc/tile_manager.cc

Index: cc/tile_manager.cc
diff --git a/cc/tile_manager.cc b/cc/tile_manager.cc
index f87fe167ef62707310cc3291331e8f430144ab95..46577fdf2a565e298b110b56d7064809b4dc44bb 100644
--- a/cc/tile_manager.cc
+++ b/cc/tile_manager.cc
@@ -396,8 +396,8 @@ void TileManager::ManageTiles() {
   // Assign gpu memory and determine what tiles need to be rasterized.
   AssignGpuMemoryToTiles();
 
-  TRACE_EVENT_INSTANT1("cc", "DidManage", "state",
-                       ValueToString(BasicStateAsValue()));
+  TRACE_EVENT_INSTANT1("cc", "DidManage", TRACE_EVENT_SCOPE_THREAD,
+                       "state", ValueToString(BasicStateAsValue()));
 
   // Finally, kick the rasterizer.
   DispatchMoreTasks();