Use int64 time stamp when storing metadata to the HTTP cache.

content/common/view_messages.h

Index: content/common/view_messages.h
diff --git a/content/common/view_messages.h b/content/common/view_messages.h
index ad09da47c55cd68ea5602a92132135bdc914a1a2..22caa25383ea4dd1fa606643a29e0da604d22eee 100644
--- a/content/common/view_messages.h
+++ b/content/common/view_messages.h
@@ -1468,10 +1468,10 @@ IPC_SYNC_MESSAGE_CONTROL3_1(ViewHostMsg_Keygen,
                             std::string /* signed public key and challenge */)
 
 // Message sent from the renderer to the browser to request that the browser
-// cache |data| associated with |url|.
+// cache |data| associated with |url| and |expected_response_time|.
 IPC_MESSAGE_CONTROL3(ViewHostMsg_DidGenerateCacheableMetadata,
                      GURL /* url */,
-                     double /* expected_response_time */,
+                     base::Time /* expected_response_time */,
                      std::vector<char> /* data */)
 
 // Register a new handler for URL requests with the given scheme.