[Downloads] Use the initiating StoragePartition for resumption.

content/public/browser/download_item.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Each download is represented by a DownloadItem, and all DownloadItems
 // are owned by the DownloadManager which maintains a global list of all
 // downloads. DownloadItems are created when a user initiates a download,
 // and exist for the duration of the browser life time.
 //
 // Download observers:
@@ skipping 174 matching lines @@
   // completed downloads, cancelled downloads, and interrupted downloads that
   // can't be resumed.
   virtual bool IsDone() const = 0;
 
   //    Origin State accessors -------------------------------------------------
 
   virtual const GURL& GetURL() const = 0;
   virtual const std::vector<GURL>& GetUrlChain() const = 0;
   virtual const GURL& GetOriginalUrl() const = 0;
   virtual const GURL& GetReferrerUrl() const = 0;
+  virtual const GURL& GetSiteInstanceUrl() const = 0;

[Charlie Reis, 2016/05/05 21:43:22]

This should really be GetSiteURL.  SiteInstance is one instance of a
Site, but the Site URL is the same for all instances of it.  (Applies throughout
the CL.)

I see that there aren't any comments in this section, but it seems like we might
want to add a comment on this saying it's used to determine StoragePartition. 
(There are many uses of SiteInstance::GetSiteURL that are currently incorrect
that nick@ is cleaning up, but this one should be safe.)

[ncarter (slow), 2016/05/05 23:29:07]

Agree that this is safe.

[asanka, 2016/05/07 00:24:45]

Cool. Thanks. I added a comment here and changed the names to
site_url/GetSiteUrl().

   virtual const GURL& GetTabUrl() const = 0;
   virtual const GURL& GetTabReferrerUrl() const = 0;
   virtual std::string GetSuggestedFilename() const = 0;
   virtual std::string GetContentDisposition() const = 0;
   virtual std::string GetMimeType() const = 0;
   virtual std::string GetOriginalMimeType() const = 0;
   virtual std::string GetRemoteAddress() const = 0;
   virtual bool HasUserGesture() const = 0;
   virtual ui::PageTransition GetTransitionType() const = 0;
   virtual const std::string& GetLastModifiedTime() const = 0;
@@ skipping 134 matching lines @@
   // return |name|. Has no effect on the final target filename.
   virtual void SetDisplayName(const base::FilePath& name) = 0;
 
   // Debug/testing -------------------------------------------------------------
   virtual std::string DebugString(bool verbose) const = 0;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_DOWNLOAD_ITEM_H_