Remove default begin frame sources from the renderer

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 @@
     SchedulerSettings scheduler_settings(
         layer_tree_host_->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()));
 
-    BeginFrameSource* frame_source = nullptr;
-    if (!layer_tree_host_->settings().use_output_surface_begin_frame_source) {
-      frame_source = external_begin_frame_source_.get();
-      if (!scheduler_settings.throttle_frame_production) {
-        // Unthrottled source takes precedence over external sources.
-        unthrottled_begin_frame_source_.reset(new BackToBackBeginFrameSource(
-            base::MakeUnique<DelayBasedTimeSource>(
-                task_runner_provider_->MainThreadTaskRunner())));
-        frame_source = unthrottled_begin_frame_source_.get();
-      }
-      if (!frame_source) {
-        synthetic_begin_frame_source_.reset(new DelayBasedBeginFrameSource(
-            base::MakeUnique<DelayBasedTimeSource>(
-                task_runner_provider_->MainThreadTaskRunner())));
-        frame_source = synthetic_begin_frame_source_.get();
-      }
-    }
-
+    // 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.

[danakj, 2016/08/16 00:30:04]

nit: Make

+    DCHECK(layer_tree_host_->settings().use_external_begin_frame_source ^
+           layer_tree_host_->settings().use_output_surface_begin_frame_source);
+    DCHECK(!layer_tree_host_->settings().use_external_begin_frame_source ||
+           external_begin_frame_source_.get());

[danakj, 2016/08/16 00:30:04]

nit: no .get()

+    DCHECK(
+        !layer_tree_host_->settings().use_output_surface_begin_frame_source ||
+        !external_begin_frame_source_.get());

[danakj, 2016/08/16 00:30:04]

nit: no .get()

     scheduler_on_impl_thread_ =
         Scheduler::Create(this, scheduler_settings, layer_tree_host_->id(),
                           task_runner_provider_->MainThreadTaskRunner(),
-                          frame_source, std::move(compositor_timing_history));
+                          external_begin_frame_source_.get(),
+                          std::move(compositor_timing_history));
   }
 
   layer_tree_host_impl_ = layer_tree_host_->CreateLayerTreeHostImpl(this);
 }
 
 SingleThreadProxy::~SingleThreadProxy() {
   TRACE_EVENT0("cc", "SingleThreadProxy::~SingleThreadProxy");
   DCHECK(task_runner_provider_->IsMainThread());
   // Make sure Stop() got called or never Started.
   DCHECK(!layer_tree_host_impl_);
@@ skipping 767 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