Convert WindowOpenDisposition to an enum class.

chrome/browser/ui/singleton_tabs.cc

Index: chrome/browser/ui/singleton_tabs.cc
diff --git a/chrome/browser/ui/singleton_tabs.cc b/chrome/browser/ui/singleton_tabs.cc
index 870e8dfbab2ddaa3153fdbc77b307a3975a62565..042f85ff071ccb64edfd13e5d99ebf6510a38ce0 100644
--- a/chrome/browser/ui/singleton_tabs.cc
+++ b/chrome/browser/ui/singleton_tabs.cc
@@ -54,7 +54,7 @@ void ShowSingletonTabOverwritingNTP(Browser* browser,
          search::IsInstantNTP(contents) ||
          contents_url == GURL(url::kAboutBlankURL)) &&
         GetIndexOfSingletonTab(&local_params) < 0) {
-      local_params.disposition = CURRENT_TAB;
+      local_params.disposition = WindowOpenDisposition::CURRENT_TAB;
     }
   }
 
@@ -64,7 +64,7 @@ void ShowSingletonTabOverwritingNTP(Browser* browser,
 NavigateParams GetSingletonTabNavigateParams(Browser* browser,
                                              const GURL& url) {
   NavigateParams params(browser, url, ui::PAGE_TRANSITION_AUTO_BOOKMARK);
-  params.disposition = SINGLETON_TAB;
+  params.disposition = WindowOpenDisposition::SINGLETON_TAB;
   params.window_action = NavigateParams::SHOW_WINDOW;
   params.user_gesture = true;
   params.tabstrip_add_types |= TabStripModel::ADD_INHERIT_OPENER;
@@ -74,7 +74,7 @@ NavigateParams GetSingletonTabNavigateParams(Browser* browser,
 // Returns the index of an existing singleton tab in |params->browser| matching
 // the URL specified in |params|.
 int GetIndexOfSingletonTab(NavigateParams* params) {
-  if (params->disposition != SINGLETON_TAB)
+  if (params->disposition != WindowOpenDisposition::SINGLETON_TAB)
     return -1;
 
   // In case the URL was rewritten by the BrowserURLHandler we need to ensure