Revert of cc::SurfaceDependencyTracker should not crash when a Display goes away

cc/surfaces/primary_begin_frame_source.h

Index: cc/surfaces/primary_begin_frame_source.h
diff --git a/cc/surfaces/primary_begin_frame_source.h b/cc/surfaces/primary_begin_frame_source.h
deleted file mode 100644
index e881a29727127e876e572e262fccb2f1c74e4af2..0000000000000000000000000000000000000000
--- a/cc/surfaces/primary_begin_frame_source.h
+++ /dev/null
@@ -1,56 +0,0 @@
-// Copyright 2017 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.
-
-#ifndef CC_SURFACES_PRIMARY_BEGIN_FRAME_SOURCE_H_
-#define CC_SURFACES_PRIMARY_BEGIN_FRAME_SOURCE_H_
-
-#include "cc/scheduler/begin_frame_source.h"
-
-namespace cc {
-
-// PrimaryBeginFrameSource echos the first BeginFrameSource in the system.
-// If the first source goes away then it will echo the new first
-// BeginFrameSource.
-class PrimaryBeginFrameSource : public BeginFrameSource,
-                                public BeginFrameObserver,
-                                public ExternalBeginFrameSourceClient {
- public:
-  PrimaryBeginFrameSource();
-  ~PrimaryBeginFrameSource() override;
-
-  void OnBeginFrameSourceAdded(BeginFrameSource* begin_frame_source);
-  void OnBeginFrameSourceRemoved(BeginFrameSource* begin_frame_source);
-
-  // BeginFrameObserver implementation.
-  void OnBeginFrame(const BeginFrameArgs& args) override;
-  const BeginFrameArgs& LastUsedBeginFrameArgs() const override;
-  void OnBeginFrameSourcePausedChanged(bool paused) override;
-
-  // BeginFrameSource implementation.
-  void DidFinishFrame(BeginFrameObserver* obs,
-                      const BeginFrameAck& ack) override;
-  void AddObserver(BeginFrameObserver* obs) override;
-  void RemoveObserver(BeginFrameObserver* obs) override;
-  bool IsThrottled() const override;
-
-  // ExternalBeginFrameSourceClient implementation.
-  void OnNeedsBeginFrames(bool needs_begin_frames) override;
-
- private:
-  ExternalBeginFrameSource begin_frame_source_;
-  BeginFrameSource* current_begin_frame_source_ = nullptr;
-
-  // The last begin frame args generated by the begin frame source.
-  BeginFrameArgs last_begin_frame_args_;
-
-  bool needs_begin_frames_ = false;
-
-  base::flat_set<BeginFrameSource*> sources_;
-
-  DISALLOW_COPY_AND_ASSIGN(PrimaryBeginFrameSource);
-};
-
-}  // namespace cc
-
-#endif  // CC_SURFACES_PRIMARY_BEGIN_FRAME_SOURCE_H_