[ios] Initialize tab strip count.

Bug: 841212
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I4cdfef554f257a7bd920aa9efba184ae8d4126ba
Reviewed-on: https://chromium-review.googlesource.com/1052549Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557275}

ios/chrome/browser/ui/tabs/tab_strip_controller.mm

@@ -1106,9 +1106,8 @@ NSString* StringForItemCount(long count) {
 }
 
 - (void)tabModelDidChangeTabCount:(TabModel*)model {
-  const NSUInteger tabCount = [_tabArray count] - [_closingTabs count];
   if (IsUIRefreshPhase1Enabled()) {
-    [_tabSwitcherButton setTitle:StringForItemCount(tabCount)
+    [_tabSwitcherButton setTitle:StringForItemCount(model.count)
                         forState:UIControlStateNormal];
   }
 }
@@ -1171,6 +1170,7 @@ NSString* StringForItemCount(long count) {
   [_tabSwitcherButton addTarget:self
                          action:@selector(recordUserMetrics:)
                forControlEvents:UIControlEventTouchUpInside];
+  [self tabModelDidChangeTabCount:_tabModel];
 
   SetA11yLabelAndUiAutomationName(_tabSwitcherButton,
                                   tabSwitcherButtonIdsAccessibilityLabel,