Replaced BackgroundAnimator with ShelfBackgroundAnimator.

ash/aura/wm_shelf_aura.cc

Index: ash/aura/wm_shelf_aura.cc
diff --git a/ash/aura/wm_shelf_aura.cc b/ash/aura/wm_shelf_aura.cc
index 25ffb6721edd3ad226d2f156a77043fc7d5f5d1e..b6024db1fed7fe2bd5dbefabb2c941df9be5c832 100644
--- a/ash/aura/wm_shelf_aura.cc
+++ b/ash/aura/wm_shelf_aura.cc
@@ -44,6 +44,14 @@ Shelf* WmShelfAura::GetShelf(WmShelf* shelf) {
   return static_cast<WmShelfAura*>(shelf)->shelf_;
 }
 
+void WmShelfAura::AddObserver(WmShelfObserver* observer) {
+  observers_.AddObserver(observer);
+}
+
+void WmShelfAura::RemoveObserver(WmShelfObserver* observer) {
+  observers_.RemoveObserver(observer);
+}
+
 void WmShelfAura::ResetShelfLayoutManager() {
   if (!shelf_layout_manager_)
     return;
@@ -93,14 +101,6 @@ gfx::Rect WmShelfAura::GetScreenBoundsOfItemIconForWindow(WmWindow* window) {
       WmWindowAura::GetAuraWindow(window));
 }
 
-void WmShelfAura::AddObserver(WmShelfObserver* observer) {
-  observers_.AddObserver(observer);
-}
-
-void WmShelfAura::RemoveObserver(WmShelfObserver* observer) {
-  observers_.RemoveObserver(observer);
-}
-
 void WmShelfAura::WillDeleteShelfLayoutManager() {
   ResetShelfLayoutManager();
 }
@@ -108,6 +108,8 @@ void WmShelfAura::WillDeleteShelfLayoutManager() {
 void WmShelfAura::OnBackgroundUpdated(
     ShelfBackgroundType background_type,
     BackgroundAnimatorChangeType change_type) {
+  if (background_type == GetBackgroundType())

[James Cook, 2016/06/14 17:50:00]

This might change when the observer fires compared to the behavior in
ShelfLayoutManager::UpdateShelfBackground(), affecting
DockedWindowLayoutManager. Are you sure this is safe?

[bruthig, 2016/07/26 19:50:01]

It most definitely changes when the WmShelfObserver is notified ;)  Before this
change the WmShelfObserver's could get spammed with notifications even when the
|background_type| didn't change.  (e.g.
ShelfLayoutManager::SetWindowOverlapsShelf() gets called for each mouse drag
event)  This is most definitely sub-optimal.

I've renamed WmShelfObserver::OnBackgroundUpdated() as OnBackgroundChanged() to
be more clear that it actually changed.  And the only two overrides of this are
in
ShelfBackgroundAnimator and DockedBackgroundWidget which only need to know if
the background type actually changed.

IMO the ShelfLayoutManager should only notify it's observers when the background
type has changed as well.  But this is not a straight forward change and it's
unclear if some observers require the current spammy behavior. However, I could
add a TODO if you'd like?

[James Cook, 2016/07/27 00:30:38]

Yes, please TODO it.

+    return;
   FOR_EACH_OBSERVER(WmShelfObserver, observers_,
                     OnBackgroundUpdated(background_type, change_type));
 }