Polish launcher tooltip visibility (2nd try).

ash/wm/shelf_layout_manager.cc

Index: ash/wm/shelf_layout_manager.cc
diff --git a/ash/wm/shelf_layout_manager.cc b/ash/wm/shelf_layout_manager.cc
index 156fad152144a9fa89d585ba5f844738e95b1512..9fe7859be50de087a72d0df11bb9b67517939bd6 100644
--- a/ash/wm/shelf_layout_manager.cc
+++ b/ash/wm/shelf_layout_manager.cc
@@ -145,6 +145,8 @@ void ShelfLayoutManager::SetAutoHideBehavior(ShelfAutoHideBehavior behavior) {
     return;
   auto_hide_behavior_ = behavior;
   UpdateVisibilityState();
+  FOR_EACH_OBSERVER(Observer, observers_,
+                    OnAutoHideStateChanged(state_.auto_hide_state));
 }
 
 bool ShelfLayoutManager::IsVisible() const {
@@ -279,6 +281,8 @@ void ShelfLayoutManager::UpdateAutoHideState() {
     if (auto_hide_state == AUTO_HIDE_HIDDEN) {
       // Hides happen immediately.
       SetState(state_.visibility_state);
+      FOR_EACH_OBSERVER(Observer, observers_,
+                        OnAutoHideStateChanged(auto_hide_state));
     } else {
       auto_hide_timer_.Stop();
       auto_hide_timer_.Start(
@@ -296,6 +300,14 @@ void ShelfLayoutManager::SetWindowOverlapsShelf(bool value) {
   UpdateShelfBackground(internal::BackgroundAnimator::CHANGE_ANIMATE);
 }
 
+void ShelfLayoutManager::AddObserver(Observer* observer) {
+  observers_.AddObserver(observer);
+}
+
+void ShelfLayoutManager::RemoveObserver(Observer* observer) {
+  observers_.RemoveObserver(observer);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // ShelfLayoutManager, aura::LayoutManager implementation:
 
@@ -345,6 +357,9 @@ void ShelfLayoutManager::SetState(VisibilityState visibility_state) {
   if (state_.Equals(state))
     return;  // Nothing changed.
 
+  FOR_EACH_OBSERVER(Observer, observers_,
+                    WillVisibilityStateChange(visibility_state));
+
   if (state.visibility_state == AUTO_HIDE) {
     // When state is AUTO_HIDE we need to track when the mouse is over the
     // launcher to unhide the shelf. AutoHideEventFilter does that for us.
@@ -507,6 +522,8 @@ bool ShelfLayoutManager::GetLauncherPaintsBackground() const {
 
 void ShelfLayoutManager::UpdateAutoHideStateNow() {
   SetState(state_.visibility_state);
+  FOR_EACH_OBSERVER(Observer, observers_, OnAutoHideStateChanged(
+      CalculateAutoHideState(state_.visibility_state)));
 }
 
 ShelfLayoutManager::AutoHideState ShelfLayoutManager::CalculateAutoHideState(