Switch Extensions::TabHelper to use WebContents, WebContentsUserData.

chrome/browser/ui/ash/launcher/browser_launcher_item_controller.cc

Index: chrome/browser/ui/ash/launcher/browser_launcher_item_controller.cc
diff --git a/chrome/browser/ui/ash/launcher/browser_launcher_item_controller.cc b/chrome/browser/ui/ash/launcher/browser_launcher_item_controller.cc
index a9268914ca9efbed3c762b600f49eee1e321c370..453df2a1aad006625364a94164f8c9023b4ec9b7 100644
--- a/chrome/browser/ui/ash/launcher/browser_launcher_item_controller.cc
+++ b/chrome/browser/ui/ash/launcher/browser_launcher_item_controller.cc
@@ -251,11 +251,11 @@ void BrowserLauncherItemController::UpdateLauncher(TabContents* tab) {
           new LauncherFaviconLoader(this, tab->web_contents()));
     }
     // Update the icon for extension panels.
+    extensions::TabHelper* extensions_tab_helper =
+        extensions::TabHelper::FromWebContents(tab->web_contents());
     SkBitmap new_image = favicon_loader_->GetFavicon();
-    if (new_image.isNull() &&
-        tab->extension_tab_helper()->GetExtensionAppIcon()) {
-      new_image = *tab->extension_tab_helper()->GetExtensionAppIcon();
-    }
+    if (new_image.isNull() && extensions_tab_helper->GetExtensionAppIcon())
+      new_image = *extensions_tab_helper->GetExtensionAppIcon();
     // Only update the icon if we have a new image, or none has been set yet.
     // This avoids flickering to an empty image when a pinned app is opened.
     if (!new_image.isNull())