Avoid string construction overhead for lookup-only HpackEntry objects.

net/spdy/hpack/hpack_decoder.cc

Index: net/spdy/hpack/hpack_decoder.cc
diff --git a/net/spdy/hpack/hpack_decoder.cc b/net/spdy/hpack/hpack_decoder.cc
index b803302c2753c9ab16cc54c30274f40c019c091f..1b66851159a6879ad006933707dd2a4c996be0b0 100644
--- a/net/spdy/hpack/hpack_decoder.cc
+++ b/net/spdy/hpack/hpack_decoder.cc
@@ -189,7 +189,7 @@ bool HpackDecoder::DecodeNextName(HpackInputStream* input_stream,
     *next_name = entry->name();
   } else {
     // |entry| could be evicted as part of this insertion. Preemptively copy.
-    key_buffer_.assign(entry->name());
+    key_buffer_.assign(entry->name().data(), entry->name().size());
     *next_name = key_buffer_;
   }
   return true;