Fixed experimental app list pagination indicator.

Was previously highlighting the wrong page (regressed in r293066) due to
the page indices not starting from 0.

ContentsSwitcherView now uses a map, not a vector, so buttons can have
arbitrary indices.

BUG=411769

Review URL: https://codereview.chromium.org/554553002

Cr-Commit-Position: refs/heads/master@{#293884}

ui/app_list/views/contents_switcher_view.cc

@@ -61,7 +61,7 @@ void ContentsSwitcherView::AddSwitcherButton(int resource_id, int page_index) {
   indicator->set_background(
       views::Background::CreateSolidBackground(app_list::kPagerSelectedColor));
   indicator->SetVisible(false);
-  page_active_indicators_.push_back(indicator);
+  page_active_indicators_[page_index] = indicator;
 
   // A container view that will consume space when its child is not visible.
   // TODO(calamity): Remove this once BoxLayout supports space-consuming
@@ -92,12 +92,14 @@ void ContentsSwitcherView::SelectedPageChanged(int old_selected,
                                                int new_selected) {
   // Makes the indicator visible when it is first drawn and when the
   // selected page is changed.
-  int num_indicators = static_cast<int>(page_active_indicators_.size());
-  if (old_selected >= 0 && old_selected < num_indicators)
-    page_active_indicators_[old_selected]->SetVisible(false);
-
-  if (new_selected >= 0 && new_selected < num_indicators)
-    page_active_indicators_[new_selected]->SetVisible(true);
+  std::map<int, views::View*>::const_iterator it =
+      page_active_indicators_.find(old_selected);
+  if (it != page_active_indicators_.end())
+    it->second->SetVisible(false);
+
+  it = page_active_indicators_.find(new_selected);
+  if (it != page_active_indicators_.end())
+    it->second->SetVisible(true);
 }
 
 void ContentsSwitcherView::TransitionStarted() {

ui/app_list/views/contents_switcher_view.h

@@ -5,6 +5,8 @@
 #ifndef UI_APP_LIST_VIEWS_CONTENTS_SWITCHER_VIEW_H_
 #define UI_APP_LIST_VIEWS_CONTENTS_SWITCHER_VIEW_H_
 
+#include <map>
+
 #include "base/basictypes.h"
 #include "ui/app_list/pagination_model_observer.h"
 #include "ui/views/controls/button/button.h"
@@ -43,8 +45,8 @@ class ContentsSwitcherView : public views::View,
 
   ContentsView* contents_view_;  // Owned by views hierarchy.
 
-  // Stores Views owned by views hierarchy.
-  std::vector<views::View*> page_active_indicators_;
+  // Maps page indices to Views owned by views hierarchy.
+  std::map<int, views::View*> page_active_indicators_;
 
   DISALLOW_COPY_AND_ASSIGN(ContentsSwitcherView);
 };