Switch Extensions::TabHelper to use WebContents, WebContentsUserData.

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

Index: chrome/browser/ui/cocoa/tabs/tab_strip_controller.mm
diff --git a/chrome/browser/ui/cocoa/tabs/tab_strip_controller.mm b/chrome/browser/ui/cocoa/tabs/tab_strip_controller.mm
index 2c1c9082490d1674b8cc2a0feea41bd595156542..b41d4c6624a51d0a7ac146de307461386c449881 100644
--- a/chrome/browser/ui/cocoa/tabs/tab_strip_controller.mm
+++ b/chrome/browser/ui/cocoa/tabs/tab_strip_controller.mm
@@ -1418,13 +1418,15 @@ private:
 // A helper routine for creating an NSImageView to hold the favicon or app icon
 // for |contents|.
 - (NSImageView*)iconImageViewForContents:(TabContents*)contents {
-  BOOL isApp = contents->extension_tab_helper()->is_app();
+  extensions::TabHelper* extensions_tab_helper =
+      extensions::TabHelper::FromWebContents(contents->web_contents());
+  BOOL isApp = extensions_tab_helper->is_app();
   NSImage* image = nil;
   // Favicons come from the renderer, and the renderer draws everything in the
   // system color space.
   CGColorSpaceRef colorSpace = base::mac::GetSystemColorSpace();
   if (isApp) {
-    SkBitmap* icon = contents->extension_tab_helper()->GetExtensionAppIcon();
+    SkBitmap* icon = extensions_tab_helper->GetExtensionAppIcon();
     if (icon)
       image = gfx::SkBitmapToNSImageWithColorSpace(*icon, colorSpace);
   } else {