ui::Compositor needs a valid FrameSinkId even when it doesn't have ContextFactoryPrivate.

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index f2d08cde512820fb5ea9af028f7e25811b276e4d..7d767d622ee369746f4e28b511cf05328f8966bb 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -85,7 +85,7 @@ Compositor::Compositor(ui::ContextFactory* context_factory,
       compositor_frame_sink_requested_(false),
       frame_sink_id_(context_factory_private
                          ? context_factory_private->AllocateFrameSinkId()
-                         : cc::FrameSinkId()),
+                         : cc::FrameSinkId(1, 1)),

[sadrul, 2016/12/16 02:29:09]

Let's have a kDefaultFrameSinkId for this. So something like:

  constexpr cc::FrameSinkId kDefaultFrameSinkId(1, 1);

up in the anon namespace. And add a comment explaining why we need a valid
sink-id here.

[mfomitchev, 2016/12/16 18:17:58]

Done.

       task_runner_(task_runner),
       vsync_manager_(new CompositorVSyncManager()),
       device_scale_factor_(0.0f),