[cc] Fix CompositorFrameSinkSupport BeginFrameAck interface.

services/ui/public/cpp/client_compositor_frame_sink.cc

Index: services/ui/public/cpp/client_compositor_frame_sink.cc
diff --git a/services/ui/public/cpp/client_compositor_frame_sink.cc b/services/ui/public/cpp/client_compositor_frame_sink.cc
index da44887cc3d03af93ac02669343579cf055c38df..b00a55452bfa8028d5d81c9a01b0aeef227be5a0 100644
--- a/services/ui/public/cpp/client_compositor_frame_sink.cc
+++ b/services/ui/public/cpp/client_compositor_frame_sink.cc
@@ -8,6 +8,7 @@
 #include "base/command_line.h"
 #include "base/memory/ptr_util.h"
 #include "cc/base/switches.h"
+#include "cc/output/begin_frame_args.h"
 #include "cc/output/compositor_frame.h"
 #include "cc/output/compositor_frame_sink_client.h"
 
@@ -77,6 +78,9 @@ void ClientCompositorFrameSink::SubmitCompositorFrame(
   if (!compositor_frame_sink_)
     return;
 
+  DCHECK_LE(cc::BeginFrameArgs::kStartingFrameNumber,
+            frame.metadata.begin_frame_ack.sequence_number);
+
   gfx::Size frame_size = last_submitted_frame_size_;
   if (!frame.render_pass_list.empty())
     frame_size = frame.render_pass_list.back()->output_rect.size();