Fix window zoom in a sane way, remove nasty casts.

chrome/browser/ui/cocoa/browser_window_controller.mm

Index: chrome/browser/ui/cocoa/browser_window_controller.mm
diff --git a/chrome/browser/ui/cocoa/browser_window_controller.mm b/chrome/browser/ui/cocoa/browser_window_controller.mm
index 1783de3efe6896660674caba89c2088c4704deba..bfe515437c3015b82d18ca0494dad636176d6c58 100644
--- a/chrome/browser/ui/cocoa/browser_window_controller.mm
+++ b/chrome/browser/ui/cocoa/browser_window_controller.mm
@@ -696,10 +696,8 @@ enum {
   if (contents) {
     // If the intrinsic width is bigger, then make it the zoomed width.
     const int kScrollbarWidth = 16;  // TODO(viettrungluu): ugh.
-    TabContentsViewMac* tab_contents_view =
-        static_cast<TabContentsViewMac*>(contents->GetView());
     CGFloat intrinsicWidth = static_cast<CGFloat>(
-        tab_contents_view->preferred_width() + kScrollbarWidth);
+        contents->GetPreferredSize().width() + kScrollbarWidth);
     zoomedWidth = std::max(zoomedWidth,
                            std::min(intrinsicWidth, frame.size.width));
   }