Move download stuff from download helper back to TabContents. This is basically a revert of r8576...

content/browser/tab_contents/tab_contents_delegate.h

Index: content/browser/tab_contents/tab_contents_delegate.h
===================================================================
--- content/browser/tab_contents/tab_contents_delegate.h	(revision 92629)
+++ content/browser/tab_contents/tab_contents_delegate.h	(working copy)
@@ -31,6 +31,7 @@
 }
 
 struct ContextMenuParams;
+class DownloadItem;
 class GURL;
 class HtmlDialogUIDelegate;
 struct NativeWebKeyboardEvent;
@@ -190,6 +191,12 @@
   // Notification that |tab_contents| has gained focus.
   virtual void TabContentsFocused(TabContents* tab_content);
 
+  // Asks the delegate if the given tab can download.
+  virtual bool CanDownload(TabContents* source, int request_id);
+
+  // Notifies the delegate that a download is starting.
+  virtual void OnStartDownload(TabContents* source, DownloadItem* download);
+
   // Return much extra vertical space should be allotted to the
   // render view widget during various animations (e.g. infobar closing).
   // This is used to make painting look smoother.