update GetHeader methods to use HttpHeaderName

Author: scotthart

google/cloud/internal/rest_context.cc

@@ -35,8 +35,8 @@ RestContext& RestContext::AddHeader(std::string header, std::string value) & {
   return AddHeader(HttpHeader(std::move(header), std::move(value)));
 }
 
-HttpHeader RestContext::GetHeader(std::string_view header) const {
-  auto iter = headers_.find(absl::AsciiStrToLower(header));
+HttpHeader RestContext::GetHeader(HttpHeaderName const& header) const {
+  auto iter = headers_.find(header);
   if (iter == headers_.end()) {
     return {};
   }

google/cloud/internal/rest_context.h

@@ -57,7 +57,7 @@ class RestContext {
   }
 
   // Header names are case-insensitive; header values are case-sensitive.
-  HttpHeader GetHeader(std::string_view header) const;
+  HttpHeader GetHeader(HttpHeaderName const& header) const;
 
   absl::optional<std::string> local_ip_address() const {
     return local_ip_address_;

google/cloud/internal/rest_request.cc

@@ -76,8 +76,8 @@ RestRequest& RestRequest::AddQueryParameter(
                            std::move(parameter.second));
 }
 
-HttpHeader RestRequest::GetHeader(std::string_view header) const {
-  auto iter = headers_.find(absl::AsciiStrToLower(header));
+HttpHeader RestRequest::GetHeader(HttpHeaderName const& header) const {
+  auto iter = headers_.find(header);
   if (iter == headers_.end()) {
     return {};
   }

google/cloud/internal/rest_request.h

@@ -83,7 +83,7 @@ class RestRequest {
 
   // Vector is empty if header name is not found.
   // Header names are case-insensitive; header values are case-sensitive.
-  HttpHeader GetHeader(std::string_view header) const;
+  HttpHeader GetHeader(HttpHeaderName const& header) const;
 
   // Returns all values associated with parameter name.
   // Parameter names and values are case-sensitive.