Don't read message-body for HEAD responses.

net/http/http_network_transaction.h

Index: net/http/http_network_transaction.h
===================================================================
--- net/http/http_network_transaction.h	(revision 10978)
+++ net/http/http_network_transaction.h	(working copy)
@@ -263,10 +263,10 @@
   // Indicates the content length remaining to read.  If this value is less
   // than zero (and chunked_decoder_ is null), then we read until the server
   // closes the connection.
-  int64 content_length_;
+  int64 response_body_length_;
 
   // Keeps track of the number of response body bytes read so far.
-  int64 content_read_;
+  int64 response_body_read_;
 
   scoped_ptr<HttpChunkedDecoder> chunked_decoder_;