Moved TabID implementation to SerializableUserData.

ios/chrome/browser/tabs/tab.mm

Index: ios/chrome/browser/tabs/tab.mm
diff --git a/ios/chrome/browser/tabs/tab.mm b/ios/chrome/browser/tabs/tab.mm
index 7dd1d6e65ed22f3cb52906c3083549605fd230e9..3e4b837fdef4b5fbf03cac9e4c04ec90da9d3715 100644
--- a/ios/chrome/browser/tabs/tab.mm
+++ b/ios/chrome/browser/tabs/tab.mm
@@ -133,6 +133,7 @@
 #include "ios/web/public/interstitials/web_interstitial.h"
 #import "ios/web/public/navigation_manager.h"
 #include "ios/web/public/referrer.h"
+#import "ios/web/public/serializable_user_data_manager.h"
 #include "ios/web/public/ssl_status.h"
 #include "ios/web/public/url_scheme_util.h"
 #include "ios/web/public/url_util.h"
@@ -176,6 +177,10 @@
 class FaviconDriverObserverBridge;
 class TabInfoBarObserver;
 
+// The key under which the Tab ID is stored in the WebState's serializable user
+// data.
+NSString* const kTabIDKey = @"TabID";
+
 // Name of histogram for recording the state of the tab when the renderer is
 // terminated.
 const char kRendererTerminationStateHistogram[] =
@@ -785,8 +790,15 @@ - (NSString*)windowName {
 }
 
 - (NSString*)tabId {
-  DCHECK([self navigationManager]);
-  return [[self navigationManager]->GetSessionController() tabId];
+  DCHECK(self.webState);
+  web::SerializableUserDataManager* userDataManager =
+      web::SerializableUserDataManager::FromWebState(self.webState);
+  id<NSCoding> tabID = userDataManager->GetValueForSerializationKey(kTabIDKey);
+  if (!tabID) {
+    tabID = [[NSUUID UUID] UUIDString];
+    userDataManager->AddSerializableData(tabID, kTabIDKey);
+  }
+  return base::mac::ObjCCastStrict<NSString>(tabID);
 }
 
 - (web::WebState*)webState {