Switch Extensions::TabHelper to use WebContents, WebContentsUserData.

chrome/browser/ui/browser_navigator.cc

Index: chrome/browser/ui/browser_navigator.cc
diff --git a/chrome/browser/ui/browser_navigator.cc b/chrome/browser/ui/browser_navigator.cc
index af2d1dc952d185232272062b770e55f8af432cdd..540ca009a41097e47f095167719dd0db3f88a8a0 100644
--- a/chrome/browser/ui/browser_navigator.cc
+++ b/chrome/browser/ui/browser_navigator.cc
@@ -132,11 +132,14 @@ Browser* GetBrowserForDisposition(chrome::NavigateParams* params) {
             params->extension_app_id);
       } else if (!params->browser->app_name().empty()) {
         app_name = params->browser->app_name();
-      } else if (params->source_contents &&
-                 params->source_contents->extension_tab_helper()->is_app()) {
-        app_name = web_app::GenerateApplicationNameFromExtensionId(
-            params->source_contents->extension_tab_helper()->
-                extension_app()->id());
+      } else if (params->source_contents) {
+        extensions::TabHelper* extensions_tab_helper =
+            extensions::TabHelper::FromWebContents(
+                params->source_contents->web_contents());
+        if (extensions_tab_helper->is_app()) {
+          app_name = web_app::GenerateApplicationNameFromExtensionId(
+              extensions_tab_helper->extension_app()->id());
+        }
       }
       if (app_name.empty()) {
         Browser::CreateParams browser_params(Browser::TYPE_POPUP, profile);
@@ -484,8 +487,9 @@ void Navigate(NavigateParams* params) {
       // This function takes ownership of |params->target_contents| until it
       // is added to a TabStripModel.
       target_contents_owner.TakeOwnership();
-      params->target_contents->extension_tab_helper()->
-          SetExtensionAppById(params->extension_app_id);
+      extensions::TabHelper::FromWebContents(
+          params->target_contents->web_contents())->
+              SetExtensionAppById(params->extension_app_id);
       // TODO(sky): figure out why this is needed. Without it we seem to get
       // failures in startup tests.
       // By default, content believes it is not hidden.  When adding contents