Revert of Use element id's for animations

cc/animation/element_id.h

Index: cc/animation/element_id.h
diff --git a/cc/animation/element_id.h b/cc/animation/element_id.h
deleted file mode 100644
index 1da52a42e19da00f9c9dcf4f4b3b2cc30a573dfb..0000000000000000000000000000000000000000
--- a/cc/animation/element_id.h
+++ /dev/null
@@ -1,81 +0,0 @@
-// 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.
-
-#ifndef CC_ANIMATION_ELEMENT_ID_H_
-#define CC_ANIMATION_ELEMENT_ID_H_
-
-#include <stddef.h>
-
-#include <cstdint>
-#include <functional>
-#include <iosfwd>
-#include <memory>
-
-#include "base/hash.h"
-#include "cc/base/cc_export.h"
-
-namespace base {
-class Value;
-namespace trace_event {
-class TracedValue;
-}  // namespace trace_event
-}  // namespace base
-
-namespace cc {
-
-namespace proto {
-class ElementId;
-}  // namespace proto
-
-// ------------------------------*IMPORTANT*---------------------------------
-// ElementId has a corresponding proto defined in cc/proto/element_id.proto.
-// When making any changes here, but sure to update the proto.
-
-// An "element" is really an animation target. It retains the name element to be
-// symmetric with ElementAnimations and blink::ElementAnimations, but is not
-// in fact tied to the notion of a blink element. It is also not associated with
-// the notion of a Layer. Ultimately, these ids will be used to look up the
-// property tree node associated with the given animation.
-//
-// These ids are chosen by cc's clients to permit the destruction and
-// restoration of cc entities (when visuals are hidden and shown) but maintain
-// stable identifiers. There will be a single layer for an ElementId, but
-// not every layer will have an id.
-struct CC_EXPORT ElementId {
-  ElementId(int primaryId, int secondaryId)
-      : primaryId(primaryId), secondaryId(secondaryId) {}
-  ElementId() : ElementId(0, 0) {}
-
-  bool operator==(const ElementId& o) const;
-  bool operator!=(const ElementId& o) const;
-  bool operator<(const ElementId& o) const;
-
-  // An ElementId's conversion to a boolean value depends only on its primaryId.
-  explicit operator bool() const;
-
-  void AddToTracedValue(base::trace_event::TracedValue* res) const;
-  std::unique_ptr<base::Value> AsValue() const;
-
-  void ToProtobuf(proto::ElementId* proto) const;
-  void FromProtobuf(const proto::ElementId& proto);
-
-  // The compositor treats this as an opaque handle and should not know how to
-  // interpret these bits. Non-blink cc clients typically operate in terms of
-  // layers and may set this value to match the client's layer id.
-  int primaryId;
-  int secondaryId;
-};
-
-CC_EXPORT ElementId LayerIdToElementIdForTesting(int layer_id);
-
-struct CC_EXPORT ElementIdHash {
-  size_t operator()(ElementId key) const;
-};
-
-// Stream operator so ElementId can be used in assertion statements.
-CC_EXPORT std::ostream& operator<<(std::ostream& out, const ElementId& id);
-
-}  // namespace cc
-
-#endif  // CC_ANIMATION_ELEMENT_ID_H_