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

crypto/secure_hash.h

Index: crypto/secure_hash.h
diff --git a/crypto/secure_hash.h b/crypto/secure_hash.h
index 491a299a3120ba276f76e2d541a09c19b05328e3..a5590e5d0b5879a14e81b75402cabd3dcc836928 100644
--- a/crypto/secure_hash.h
+++ b/crypto/secure_hash.h
@@ -10,11 +10,6 @@
 #include "base/macros.h"
 #include "crypto/crypto_export.h"
 
-namespace base {
-class Pickle;
-class PickleIterator;
-}
-
 namespace crypto {
 
 // A wrapper to calculate secure hashes incrementally, allowing to
@@ -30,17 +25,12 @@ class CRYPTO_EXPORT SecureHash {
 
   virtual void Update(const void* input, size_t len) = 0;
   virtual void Finish(void* output, size_t len) = 0;
+  virtual size_t GetHashLength() const = 0;
 
-  // Serialize the context, so it can be restored at a later time.
-  // |pickle| will contain the serialized data.
-  // Returns whether or not |pickle| was filled.
-  virtual bool Serialize(base::Pickle* pickle) = 0;
-
-  // Restore the context that was saved earlier.
-  // |data_iterator| allows this to be used as part of a larger pickle.
-  // |pickle| holds the saved data.
-  // Returns success or failure.
-  virtual bool Deserialize(base::PickleIterator* data_iterator) = 0;
+  // Create a clone of this SecureHash. The returned clone and this both
+  // represent the same hash state. But from this point on, calling
+  // Update()/Finish() on either doesn't affect the state of the other.
+  virtual SecureHash* Clone() const = 0;
 
  protected:
   SecureHash() {}