alternate ntp: implement Show/HideBars API to reduce jank when showing/hiding bars

chrome/browser/infobars/infobar_container.cc

Index: chrome/browser/infobars/infobar_container.cc
diff --git a/chrome/browser/infobars/infobar_container.cc b/chrome/browser/infobars/infobar_container.cc
index b601744e09fac3f45aca280186dab6b1d419ac9d..cccb5595ae2b262c104394758c7000bc7bc76733 100644
--- a/chrome/browser/infobars/infobar_container.cc
+++ b/chrome/browser/infobars/infobar_container.cc
@@ -45,17 +45,20 @@ InfoBarContainer::~InfoBarContainer() {
 }
 
 void InfoBarContainer::ChangeInfoBarService(InfoBarService* infobar_service) {
-  registrar_.RemoveAll();
+  HideAllInfoBars();

[Peter Kasting, 2013/03/16 00:40:59]

We don't need to do this here.  If the search model says the top bars aren't
visible, then we must have gotten a call to ModelChanged() in the past at the
time we wanted to make the bars invisible, which would have hidden all the bars.
 Since then, we've never re-added any bars because this function will early-exit
and Observe() won't be reached (since we're not listening to any notifications).
 So there will never be any bars visible in that case, hence the early exit
before calling HideAllBars() is OK.

[kuan, 2013/03/18 15:37:29]

switching between tabs doesn't work correctly if i don't call HideAllInfoBars().
this is the scenario i tried:
1) forced a crash infobar
2) open 1st ntp, crash infobar shows: expected
3) open 2nd ntp, crash infobar still shows: this is incorrect - crash infobar
shld not show up for subsequent tabs
4) switch back to 1st tab: ChangeInfoBarService crashes due to duplicate
registration when adding notifications to registrar. 

the scenario doesn't trigger or involve ModelChanged from 1993. 
ChangeInfoBarService is called at steps 2 to 4 from
BrowserView::ActiveTabChanged, with search_model_->top_bars_visible() being
true.

+
+  infobar_service_ = infobar_service;
+
+  if (search_model_ && !search_model_->top_bars_visible())
+    return;
 
   // Note that HideAllInfoBars() sets |infobars_shown_| to false, because that's
   // what the other, Instant-related callers want; but here we actually
   // explicitly want to reset this variable to true.  So do that after calling
   // the function.
-  HideAllInfoBars();
   infobars_shown_ = true;
   infobars_shown_time_ = base::TimeTicks();
 
-  infobar_service_ = infobar_service;
   if (infobar_service_) {
     content::Source<InfoBarService> source(infobar_service_);
     registrar_.Add(this, chrome::NOTIFICATION_TAB_CONTENTS_INFOBAR_ADDED,
@@ -138,12 +141,8 @@ void InfoBarContainer::RemoveAllInfoBarsForDestruction() {
 void InfoBarContainer::Observe(int type,
                                const content::NotificationSource& source,
                                const content::NotificationDetails& details) {
-  // When infobars are supposed to be hidden, we shouldn't try to hide or show
-  // anything in response to any notifications.  Once infobars get un-hidden
-  // via ChangeInfoBarService(), we'll get the updated set of visible infobars
-  // from the InfoBarService.
-  if (!infobars_shown_)
-    return;
+  // When infobars are hidden, we shouldn't be listening for notifications.
+  DCHECK(infobars_shown_);
 
   switch (type) {
     case chrome::NOTIFICATION_TAB_CONTENTS_INFOBAR_ADDED:
@@ -174,29 +173,17 @@ void InfoBarContainer::Observe(int type,
   }
 }
 
-void InfoBarContainer::ModeChanged(const chrome::search::Mode& old_mode,
-                                   const chrome::search::Mode& new_mode) {
-  // Hide infobars when showing Instant Extended suggestions.
-  if (new_mode.is_search_suggestions()) {
-    // If suggestions are being shown on a |DEFAULT| page, delay the hiding
-    // until notification that Instant overlay is ready is received via
-    // OverlayStateChanged(); this prevents jankiness caused by infobars hiding
-    // followed by suggestions appearing.
-    if (new_mode.is_origin_default())
-      return;
-    HideAllInfoBars();
-    OnInfoBarStateChanged(false);
-  } else {
+void InfoBarContainer::ModelChanged(
+    const chrome::search::SearchModel::State& old_state,
+    const chrome::search::SearchModel::State& new_state) {
+  if (!chrome::search::SearchModel::ShouldChangeTopBarsVisibility(old_state,
+                                                                  new_state))
+    return;
+
+  if (new_state.top_bars_visible && !infobars_shown_) {
     ChangeInfoBarService(infobar_service_);
     infobars_shown_time_ = base::TimeTicks::Now();
-  }
-}
-
-void InfoBarContainer::OverlayStateChanged(const InstantOverlayModel& model) {
-  // If suggestions are being shown on a |DEFAULT| page, hide the infobars now.
-  // See comments for ModeChanged() for explanation.
-  if (model.mode().is_search_suggestions() &&
-      model.mode().is_origin_default()) {
+  } else if (!new_state.top_bars_visible && infobars_shown_) {
     HideAllInfoBars();
     OnInfoBarStateChanged(false);
   }
@@ -229,6 +216,8 @@ size_t InfoBarContainer::HideInfoBar(InfoBarDelegate* delegate,
 }
 
 void InfoBarContainer::HideAllInfoBars() {
+  registrar_.RemoveAll();
+
   infobars_shown_ = false;
   while (!infobars_.empty()) {
     InfoBar* infobar = infobars_.front();