Remove uses of external begin frame sources

cc/trees/single_thread_proxy.cc

 // Copyright 2011 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/trees/single_thread_proxy.h"
 
 #include "base/auto_reset.h"
 #include "base/memory/ptr_util.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 56 matching lines @@
   if (settings.single_thread_proxy_scheduler && !scheduler_on_impl_thread_) {
     SchedulerSettings scheduler_settings(settings.ToSchedulerSettings());
     scheduler_settings.commit_to_active_tree = CommitToActiveTree();
 
     std::unique_ptr<CompositorTimingHistory> compositor_timing_history(
         new CompositorTimingHistory(
             scheduler_settings.using_synchronous_renderer_compositor,
             CompositorTimingHistory::BROWSER_UMA,
             layer_tree_host_->rendering_stats_instrumentation()));
 
-    // BFS must either be external or come from the output surface.  If
-    // external, it must be provided.  If from the output surface, it must
-    // not be provided.
-    // TODO(enne): Make all BFS come from the output surface.
-    DCHECK(settings.use_external_begin_frame_source ^
-           settings.use_output_surface_begin_frame_source);
-    DCHECK(!settings.use_external_begin_frame_source ||
-           external_begin_frame_source_);
-    DCHECK(!settings.use_output_surface_begin_frame_source ||
-           !external_begin_frame_source_);
+    // TODO(enne): remove these settings.
+    DCHECK(!settings.use_external_begin_frame_source);
+    DCHECK(settings.use_output_surface_begin_frame_source);
     scheduler_on_impl_thread_ =
         Scheduler::Create(this, scheduler_settings, layer_tree_host_->GetId(),
                           task_runner_provider_->MainThreadTaskRunner(),
                           external_begin_frame_source_.get(),
                           std::move(compositor_timing_history));
   }
 
   layer_tree_host_impl_ = layer_tree_host_->CreateLayerTreeHostImpl(this);
 }
 
@@ skipping 667 matching lines @@
 void SingleThreadProxy::DidFinishImplFrame() {
   layer_tree_host_impl_->DidFinishImplFrame();
 #if DCHECK_IS_ON()
   DCHECK(inside_impl_frame_)
       << "DidFinishImplFrame called while not inside an impl frame!";
   inside_impl_frame_ = false;
 #endif
 }
 
 }  // namespace cc