Replace QuicString with std::string, pass 1

This replaces QuicString with std::string in all of the "QUIC proper".  I will
delete QuicString once all code using it is gone.

gfe-relnote: n/a (no functional change)
PiperOrigin-RevId: 237872023
Change-Id: I82de62c9855516b15039734d05155917e68ff4ee
diff --git a/quic/core/qpack/qpack_encoder_stream_sender.cc b/quic/core/qpack/qpack_encoder_stream_sender.cc
index fb43046..6cd458a 100644
--- a/quic/core/qpack/qpack_encoder_stream_sender.cc
+++ b/quic/core/qpack/qpack_encoder_stream_sender.cc
@@ -28,7 +28,7 @@
 
   instruction_encoder_.Encode(InsertWithNameReferenceInstruction());
 
-  QuicString output;
+  std::string output;
 
   instruction_encoder_.Next(std::numeric_limits<size_t>::max(), &output);
   DCHECK(!instruction_encoder_.HasNext());
@@ -44,7 +44,7 @@
 
   instruction_encoder_.Encode(InsertWithoutNameReferenceInstruction());
 
-  QuicString output;
+  std::string output;
 
   instruction_encoder_.Next(std::numeric_limits<size_t>::max(), &output);
   DCHECK(!instruction_encoder_.HasNext());
@@ -57,7 +57,7 @@
 
   instruction_encoder_.Encode(DuplicateInstruction());
 
-  QuicString output;
+  std::string output;
 
   instruction_encoder_.Next(std::numeric_limits<size_t>::max(), &output);
   DCHECK(!instruction_encoder_.HasNext());
@@ -70,7 +70,7 @@
 
   instruction_encoder_.Encode(SetDynamicTableCapacityInstruction());
 
-  QuicString output;
+  std::string output;
 
   instruction_encoder_.Next(std::numeric_limits<size_t>::max(), &output);
   DCHECK(!instruction_encoder_.HasNext());