[Downloads] Introduce GUIDs for downloads.

content/public/browser/download_manager.h

Index: content/public/browser/download_manager.h
diff --git a/content/public/browser/download_manager.h b/content/public/browser/download_manager.h
index b53151ac91dc10bbf8b3ea626b586346e0344329..565a425f081d0b34a85b4302e954188446d9b5ea 100644
--- a/content/public/browser/download_manager.h
+++ b/content/public/browser/download_manager.h
@@ -139,6 +139,7 @@ class CONTENT_EXPORT DownloadManager : public base::SupportsUserData::Data {
   // Called by the embedder, after creating the download manager, to let it know
   // about downloads from previous runs of the browser.
   virtual DownloadItem* CreateDownloadItem(
+      const std::string& guid,
       uint32_t id,
       const base::FilePath& current_path,
       const base::FilePath& target_path,
@@ -177,7 +178,13 @@ class CONTENT_EXPORT DownloadManager : public base::SupportsUserData::Data {
 
   // Get the download item for |id| if present, no matter what type of download
   // it is or state it's in.
+  // DEPRECATED: Don't add new callers for GetDownload(uint32_t). Instead keep
+  // track of the GUID and use GetDownloadByGuid(), or observe the DownloadItem
+  // if you need to keep track of a specific download. (http://crbug.com/593020)
   virtual DownloadItem* GetDownload(uint32_t id) = 0;
+
+  // Get the download item for |guid|.
+  virtual DownloadItem* GetDownloadByGuid(const std::string& guid) = 0;
 };
 
 }  // namespace content