Use net's response header parser for parsing multipart headers.

net/http/http_util.h

Index: net/http/http_util.h
diff --git a/net/http/http_util.h b/net/http/http_util.h
index b1585243d3eb0db4b267a0425367012e273a864a..59c9f7d3e9bec05f07eeedbc7dd3b2b02dfb5801 100644
--- a/net/http/http_util.h
+++ b/net/http/http_util.h
@@ -151,6 +151,12 @@ class NET_EXPORT HttpUtil {
   // The parameter |i| is the offset within |buf| to begin searching from.
   static int LocateEndOfHeaders(const char* buf, int buf_len, int i = 0);
 
+  // Same as |LocateEndOfHeaders| with the difference that it detects
+  // an empty header list if |buf| starts with a single [CR]LF.

[mmenke, 2015/06/09 20:23:37]

Suggest focusing on what it's used for, rather than what it does.  Maybe
something like:

"Same as |LocateEndOfHeaders|, but does not expect a status line, so can be used
on multi-part responses or HTTP/1.x trailers.  As a result, if |buf| starts with
a single [CR]LF,  it is considered an empty header list, as opposed to an empty
status line above a header list."

[haavardm, 2015/06/10 11:54:02]

Agree. I didn't take the http status into the equation here, but it makes sense
to do so. 

+  static int LocateEndOfAdditionalHeaders(const char* buf,
+                                          int buf_len,
+                                          int i = 0);
+
   // Assemble "raw headers" in the format required by HttpResponseHeaders.
   // This involves normalizing line terminators, converting [CR]LF to \0 and
   // handling HTTP line continuations (i.e., lines starting with LWS are