Refactor StringPiece hash.

net/quic/quic_blocked_writer_interface.h

Index: net/quic/quic_blocked_writer_interface.h
diff --git a/net/quic/quic_blocked_writer_interface.h b/net/quic/quic_blocked_writer_interface.h
index 78a270af12f685636bf3bf495b5965e3a9ca6ae6..a3a2622a599d561a226371b6b888b2b3e5a9903f 100644
--- a/net/quic/quic_blocked_writer_interface.h
+++ b/net/quic/quic_blocked_writer_interface.h
@@ -24,20 +24,15 @@ class NET_EXPORT_PRIVATE QuicBlockedWriterInterface {
   virtual void OnCanWrite() = 0;
 };
 
-}  // namespace net
-
-#if defined(COMPILER_GCC)

[Bence, 2016/02/04 16:32:00]

I believe that this hash<> specialization was originally added only to GCC
because of library issues, then it was just a plain hash<size_t>(ptr).  Then it
was improved to bring more entropy to the lower bits, see
https://crrev.com/467963002/diff/20001/net/quic/quic_dispatcher.h#newcode31.  It
makes sense to have this improvement on all platforms.

[davidben, 2016/02/04 19:45:09]

+rch should probably review the QUIC bits, especially because of the complex
relationship with the internal codebase. Also note that this change requires
updating all the consumers of this hash. It looks like this patch gets all of
them, but rch should probably double-check.

[Ryan Hamilton, 2016/02/04 20:15:14]

Interestingly, the internal version does not need this specialization so this
code is only in the chromium version.

-namespace BASE_HASH_NAMESPACE {
 // Hash pointers as if they were int's, but bring more entropy to the lower
 // bits.
-template <>
-struct hash<net::QuicBlockedWriterInterface*> {
+struct QuicBlockedWriterInterfacePtrHash {
   std::size_t operator()(const net::QuicBlockedWriterInterface* ptr) const {
     size_t k = reinterpret_cast<size_t>(ptr);
     return k + (k >> 6);
   }
 };
-}
-#endif
+
+}  // namespace net
 
 #endif  // NET_QUIC_QUIC_BLOCKED_WRITER_INTERFACE_H_