Remove fields that are unused and reference classes that do not exist.

chrome/browser/cocoa/throbber_view.mm

Index: chrome/browser/cocoa/throbber_view.mm
diff --git a/chrome/browser/cocoa/throbber_view.mm b/chrome/browser/cocoa/throbber_view.mm
index d31b719a98846c0faf6a3c02695d17aeec55bca5..5a500340b24786794c09da0c4d7854f54c82e7a9 100644
--- a/chrome/browser/cocoa/throbber_view.mm
+++ b/chrome/browser/cocoa/throbber_view.mm
@@ -353,8 +353,8 @@ typedef std::set<ThrobberView*> ThrobberSet;
   [super viewDidUnhide];
 }
 
-// Called when the ThrobberTimerTarget gets tickled by our timer. Advance the
-// frame, dirty the display, and kill the timer when it's no longer needed.
+// Called when the timer fires. Advance the frame, dirty the display, and remove
+// the throbber if it's no longer needed.
 - (void)animate {
   [dataDelegate_ advanceFrame];
   [self setNeedsDisplay:YES];