Add simple non-response-based question parsing for mDNS passive listening

net/dns/dns_response.h

Index: net/dns/dns_response.h
diff --git a/net/dns/dns_response.h b/net/dns/dns_response.h
index 78fb73571028ad6fa3e47d2f81eaf1516e373372..e918b4568a6048dc26cc5079521c18826329964f 100644
--- a/net/dns/dns_response.h
+++ b/net/dns/dns_response.h
@@ -115,6 +115,10 @@ class NET_EXPORT_PRIVATE DnsResponse {
   // packet matches the |query| id and question.
   bool InitParse(int nbytes, const DnsQuery& query);
 
+  // Assuming the internal buffer holds |nbytes| bytes, initialize the parser
+  // without matching it against an existing query.
+  bool InitParse(int nbytes);
+
   // Returns true if response is valid, that is, after successful InitParse.
   bool IsValid() const;
 
@@ -132,6 +136,9 @@ class NET_EXPORT_PRIVATE DnsResponse {
   // Returns qname in dotted format.
   std::string GetDottedName() const;
 
+  // Returns the offset of the response.
+  size_t GetResponseOffset() const;
+
   // Returns an iterator to the resource records in the answer section.
   // The iterator is valid only in the scope of the DnsResponse.
   // This operation is idempotent.