Remove parts of //cc we aren't using

cc/base/synced_property.h

-// Copyright 2014 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_BASE_SYNCED_PROPERTY_H_
-#define CC_BASE_SYNCED_PROPERTY_H_
-
-#include "base/memory/ref_counted.h"
-
-namespace cc {
-
-// This class is the basic primitive used for impl-thread scrolling.  Its job is
-// to sanely resolve the case where both the main and impl thread are
-// concurrently updating the same value (for example, when Javascript sets the
-// scroll offset during an ongoing impl-side scroll).
-//
-// There are three trees (main, pending, and active) and therefore also three
-// places with their own idea of the scroll offsets (and analogous properties
-// like page scale).  Objects of this class are meant to be held on the Impl
-// side, and contain the canonical reference for the pending and active trees,
-// as well as keeping track of the latest delta sent to the main thread (which
-// is necessary for conflict resolution).
-
-template <typename T>
-class SyncedProperty : public base::RefCounted<SyncedProperty<T>> {
- public:
-  SyncedProperty() : clobber_active_value_(false) {}
-
-  // Returns the canonical value for the specified tree, including the sum of
-  // all deltas.  The pending tree should use this for activation purposes and
-  // the active tree should use this for drawing.
-  typename T::ValueType Current(bool is_active_tree) const {
-    if (is_active_tree)
-      return active_base_.Combine(active_delta_).get();
-    else
-      return pending_base_.Combine(PendingDelta()).get();
-  }
-
-  // Sets the value on the impl thread, due to an impl-thread-originating
-  // action.  Returns true if this had any effect.  This will remain
-  // impl-thread-only information at first, and will get pulled back to the main
-  // thread on the next call of PullDeltaToMainThread (which happens right
-  // before the commit).
-  bool SetCurrent(typename T::ValueType current) {
-    T delta = T(current).InverseCombine(active_base_);
-    if (active_delta_.get() == delta.get())
-      return false;
-
-    active_delta_ = delta;
-    return true;
-  }
-
-  // Returns the difference between the last value that was committed and
-  // activated from the main thread, and the current total value.
-  typename T::ValueType Delta() const { return active_delta_.get(); }
-
-  // Returns the latest active tree delta and also makes a note that this value
-  // was sent to the main thread.
-  typename T::ValueType PullDeltaForMainThread() {
-    sent_delta_ = active_delta_;
-    return active_delta_.get();
-  }
-
-  // Push the latest value from the main thread onto pending tree-associated
-  // state.  Returns true if this had any effect.
-  bool PushFromMainThread(typename T::ValueType main_thread_value) {
-    if (pending_base_.get() == main_thread_value)
-      return false;
-
-    pending_base_ = T(main_thread_value);
-
-    return true;
-  }
-
-  // Push the value associated with the pending tree to be the active base
-  // value.  As part of this, subtract the last sent value from the active tree
-  // delta (which will make the delta zero at steady state, or make it contain
-  // only the difference since the last send).
-  bool PushPendingToActive() {
-    if (active_base_.get() == pending_base_.get() &&
-        sent_delta_.get() == T::Identity().get())
-      return false;
-
-    active_base_ = pending_base_;
-    active_delta_ = PendingDelta();
-    sent_delta_ = T::Identity();
-    clobber_active_value_ = false;
-
-    return true;
-  }
-
-  // This simulates the consequences of the sent value getting committed and
-  // activated.  The value sent to the main thread ends up combined with the
-  // active value, and the sent_delta is subtracted from the delta.
-  void AbortCommit() {
-    active_base_ = active_base_.Combine(sent_delta_);
-    active_delta_ = PendingDelta();
-    sent_delta_ = T::Identity();
-  }
-
-  // Values as last pushed to the pending or active tree respectively, with no
-  // impl-thread delta applied.
-  typename T::ValueType PendingBase() const { return pending_base_.get(); }
-  typename T::ValueType ActiveBase() const { return active_base_.get(); }
-
-  // The new delta we would use if we decide to activate now.  This delta
-  // excludes the amount that we expect the main thread to reflect back at the
-  // impl thread during the commit.
-  T PendingDelta() const {
-    if (clobber_active_value_)
-      return T::Identity();
-    return active_delta_.InverseCombine(sent_delta_);
-  }
-
-  void set_clobber_active_value() { clobber_active_value_ = true; }
-
- private:
-  // Value last committed to the pending tree.
-  T pending_base_;
-  // Value last committed to the active tree (on the last activation).
-  T active_base_;
-  // The difference between the active_base_ and the user-perceived value.
-  T active_delta_;
-  // The value sent to the main thread (on the last BeginFrame); this is always
-  // identity outside of the BeginFrame-to-activation interval.
-  T sent_delta_;
-  // When true the pending delta is always identity so that it does not change
-  // and will clobber the active value on push.
-  bool clobber_active_value_;
-
-  friend class base::RefCounted<SyncedProperty<T>>;
-  ~SyncedProperty() {}
-};
-
-// SyncedProperty's delta-based conflict resolution logic makes sense for any
-// mathematical group.  In practice, there are two that are useful:
-// 1. Numbers/vectors with addition and identity = 0 (like scroll offsets)
-// 2. Real numbers with multiplication and identity = 1 (like page scale)
-
-template <class V>
-class AdditionGroup {
- public:
-  typedef V ValueType;
-
-  AdditionGroup() : value_(Identity().get()) {}
-  explicit AdditionGroup(V value) : value_(value) {}
-
-  V& get() { return value_; }
-  const V& get() const { return value_; }
-
-  static AdditionGroup<V> Identity() { return AdditionGroup(V()); }  // zero
-  AdditionGroup<V> Combine(AdditionGroup<V> p) const {
-    return AdditionGroup<V>(value_ + p.value_);
-  }
-  AdditionGroup<V> InverseCombine(AdditionGroup<V> p) const {
-    return AdditionGroup<V>(value_ - p.value_);
-  }
-
- private:
-  V value_;
-};
-
-class ScaleGroup {
- public:
-  typedef float ValueType;
-
-  ScaleGroup() : value_(Identity().get()) {}
-  explicit ScaleGroup(float value) : value_(value) {}
-
-  float& get() { return value_; }
-  const float& get() const { return value_; }
-
-  static ScaleGroup Identity() { return ScaleGroup(1.f); }
-  ScaleGroup Combine(ScaleGroup p) const {
-    return ScaleGroup(value_ * p.value_);
-  }
-  ScaleGroup InverseCombine(ScaleGroup p) const {
-    return ScaleGroup(value_ / p.value_);
-  }
-
- private:
-  float value_;
-};
-
-}  // namespace cc
-
-#endif  // CC_BASE_SYNCED_PROPERTY_H_