Clean up TCW, make it solely a hub for 1:1 observer/helper objects.

chrome/browser/ui/cocoa/constrained_window_mac.mm

Index: chrome/browser/ui/cocoa/constrained_window_mac.mm
diff --git a/chrome/browser/ui/cocoa/constrained_window_mac.mm b/chrome/browser/ui/cocoa/constrained_window_mac.mm
index bed37c86a7158d96afd9219bd1ea6ed0bf8eab4f..16f02145dce2b82227d496cd6ead132cf2778a91 100644
--- a/chrome/browser/ui/cocoa/constrained_window_mac.mm
+++ b/chrome/browser/ui/cocoa/constrained_window_mac.mm
@@ -105,7 +105,8 @@ void ConstrainedWindowMac::ShowConstrainedWindow() {
   // The TabContents only has a native window if it is currently visible. In
   // this case, open the sheet now. Else, Realize() will be called later, when
   // our tab becomes visible.
-  NSWindow* browserWindow = wrapper_->view()->GetTopLevelNativeWindow();
+  NSWindow* browserWindow =
+      wrapper_->tab_contents()->view()->GetTopLevelNativeWindow();
   NSWindowController* controller = [browserWindow windowController];
   if (controller != nil) {
     DCHECK([controller isKindOfClass:[BrowserWindowController class]]);