Makes the current page dim out when transitioning to instant preview.

chrome/browser/instant/instant_delegate.h

Index: chrome/browser/instant/instant_delegate.h
diff --git a/chrome/browser/instant/instant_delegate.h b/chrome/browser/instant/instant_delegate.h
index a5c922359c7c210f67a3bbb840519286381712d4..90f58a2cf6925c8bc983e6ac2da455d8b8e53ac0 100644
--- a/chrome/browser/instant/instant_delegate.h
+++ b/chrome/browser/instant/instant_delegate.h
@@ -18,6 +18,11 @@ class Rect;
 // InstantController for details.
 class InstantDelegate {
  public:
+  // Invoked when instant starts loading, but before the preview tab contents is
+  // ready to be shown. This may be used to animate between the states.
+  // This is followed by ShowInstant and/or HideInstant.
+  virtual void PrepareForInstant() = 0;
+
   // Invoked when the instant TabContents should be shown.
   virtual void ShowInstant(TabContents* preview_contents) = 0;