Add SpdyString alias for std::string in net/spdy.

net/spdy/spdy_header_indexing.cc

Index: net/spdy/spdy_header_indexing.cc
diff --git a/net/spdy/spdy_header_indexing.cc b/net/spdy/spdy_header_indexing.cc
index 948b5a84ec440ab4fc85b7a331832a32328564f1..881ba86754406fe885fc2a28e30faacbaffc62db 100644
--- a/net/spdy/spdy_header_indexing.cc
+++ b/net/spdy/spdy_header_indexing.cc
@@ -21,7 +21,7 @@ HeaderIndexing::HeaderIndexing()
 HeaderIndexing::~HeaderIndexing() {}
 
 void HeaderIndexing::CreateInitIndexingHeaders() {
-  const std::string initial_fields[] = {
+  const SpdyString initial_fields[] = {
       // Estimated top 100 fields.
       "alt-svc",
       "date",
@@ -139,7 +139,7 @@ bool HeaderIndexing::ShouldIndex(SpdyStringPiece header,
     return false;
   }
   // header is in indexing set.
-  std::string header_str(header.data(), header.size());
+  SpdyString header_str(header.data(), header.size());
   if (indexing_set_.find(header_str) != indexing_set_.end()) {
     return true;
   }
@@ -156,7 +156,7 @@ bool HeaderIndexing::ShouldIndex(SpdyStringPiece header,
   return false;
 }
 
-void HeaderIndexing::TryInsertHeader(std::string&& header,
+void HeaderIndexing::TryInsertHeader(SpdyString&& header,
                                      HeaderSet* set,
                                      size_t bound) {
   std::pair<HeaderSet::iterator, bool> result = set->insert(std::move(header));