[ash-md] Remove the number of animators used for the Shelf animations.

ash/common/wm/background_animator.cc

-// Copyright (c) 2012 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 "ash/common/wm/background_animator.h"
-
-namespace ash {
-namespace {
-
-// Duration of the background animation.
-const int kBackgroundDurationMS = 1000;
-}
-
-BackgroundAnimator::BackgroundAnimator(BackgroundAnimatorDelegate* delegate,
-                                       int min_alpha,
-                                       int max_alpha)
-    : delegate_(delegate),
-      min_alpha_(min_alpha),
-      max_alpha_(max_alpha),
-      animation_(this),
-      paints_background_(false),
-      alpha_(min_alpha) {
-  animation_.SetSlideDuration(kBackgroundDurationMS);
-}
-
-BackgroundAnimator::~BackgroundAnimator() {}
-
-void BackgroundAnimator::SetDuration(int time_in_ms) {
-  animation_.SetSlideDuration(time_in_ms);
-}
-
-void BackgroundAnimator::Stop() {
-  animation_.Stop();
-}
-
-void BackgroundAnimator::SetPaintsBackground(
-    bool value,
-    BackgroundAnimatorChangeType type) {
-  if (paints_background_ == value)
-    return;
-  paints_background_ = value;
-  if (type == BACKGROUND_CHANGE_IMMEDIATE && !animation_.is_animating()) {
-    animation_.Reset(value ? 1.0f : 0.0f);
-    AnimationProgressed(&animation_);
-    AnimationEnded(&animation_);
-    return;
-  }
-  if (paints_background_)
-    animation_.Show();
-  else
-    animation_.Hide();
-}
-
-void BackgroundAnimator::AnimationProgressed(const gfx::Animation* animation) {
-  int alpha = animation->CurrentValueBetween(min_alpha_, max_alpha_);
-  if (alpha_ == alpha)
-    return;
-  alpha_ = alpha;
-  delegate_->UpdateBackground(this, alpha_);
-}
-
-void BackgroundAnimator::AnimationEnded(const gfx::Animation* animation) {
-  delegate_->BackgroundAnimationEnded(this);
-}
-
-}  // namespace ash