Reject frames with invalid BeginFrameAck in CompositorFrameSinkSupport

cc/surfaces/compositor_frame_sink_support.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/surfaces/compositor_frame_sink_support.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "cc/output/compositor_frame.h"
@@ skipping 107 matching lines @@
   if (begin_frame_source_)
     begin_frame_source_->DidFinishFrame(this, ack);
 }
 
 void CompositorFrameSinkSupport::SubmitCompositorFrame(
     const LocalSurfaceId& local_surface_id,
     CompositorFrame frame) {
   DCHECK(surface_factory_);
   ++ack_pending_count_;
 
-  if (frame.metadata.begin_frame_ack.sequence_number <
-      BeginFrameArgs::kStartingFrameNumber) {
-    DLOG(ERROR) << "Received CompositorFrame with invalid BeginFrameAck.";
-    frame.metadata.begin_frame_ack.source_id = BeginFrameArgs::kManualSourceId;
-    frame.metadata.begin_frame_ack.sequence_number =
-        BeginFrameArgs::kStartingFrameNumber;
-  }
+  DCHECK_GE(frame.metadata.begin_frame_ack.sequence_number,
+            BeginFrameArgs::kStartingFrameNumber);
+
   // |has_damage| is not transmitted.
   frame.metadata.begin_frame_ack.has_damage = true;
 
   BeginFrameAck ack = frame.metadata.begin_frame_ack;
   surface_factory_->SubmitCompositorFrame(
       local_surface_id, std::move(frame),
       base::Bind(&CompositorFrameSinkSupport::DidReceiveCompositorFrameAck,
                  weak_factory_.GetWeakPtr()),
       base::BindRepeating(&CompositorFrameSinkSupport::WillDrawSurface,
                           weak_factory_.GetWeakPtr()));
@@ skipping 129 matching lines @@
     begin_frame_source_->RemoveObserver(this);
 }
 
 void CompositorFrameSinkSupport::RequestCopyOfSurface(
     std::unique_ptr<CopyOutputRequest> request) {
   DCHECK(surface_factory_);
   surface_factory_->RequestCopyOfSurface(std::move(request));
 }
 
 }  // namespace cc