[Downloads] Rework how hashes are calculated for download files.

content/public/browser/download_item.h

Index: content/public/browser/download_item.h
diff --git a/content/public/browser/download_item.h b/content/public/browser/download_item.h
index d3a7798a019b6f6976de26e6d3cdaaaaebc9e344..f95547865b62aa1338532b0992b9457fbadf233c 100644
--- a/content/public/browser/download_item.h
+++ b/content/public/browser/download_item.h
@@ -82,8 +82,6 @@ class CONTENT_EXPORT DownloadItem : public base::SupportsUserData {
 
   static const uint32_t kInvalidId;
 
-  static const char kEmptyFileHash[];
-
   // Interface that observers of a particular download must implement in order
   // to receive updates to the download's status.
   class CONTENT_EXPORT Observer {
@@ -228,13 +226,10 @@ class CONTENT_EXPORT DownloadItem : public base::SupportsUserData {
 
   virtual TargetDisposition GetTargetDisposition() const = 0;
 
-  // Final hash of completely downloaded file; not valid if
-  // GetState() != COMPLETED.
+  // Final hash of completely downloaded file, or partial hash of an interrupted
+  // download; only valid if GetState() == COMPLETED or INTERRUPTED.
   virtual const std::string& GetHash() const = 0;
 
-  // Intermediate hash state, for persisting partial downloads.
-  virtual const std::string& GetHashState() const = 0;
-
   // True if the file associated with the download has been removed by
   // external action.
   virtual bool GetFileExternallyRemoved() const = 0;