Add more Signed Exchange header constants

Add more Signed Exchange header constants, as identified in
r556931, for consistency.

Bug: 803774
Change-Id: Icbf559670bad539fa618b9a5e98eceb39095d2df
Reviewed-on: https://chromium-review.googlesource.com/1051238Reviewed-by: Tsuyoshi Horo <horo@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Rob Buis <rbuis@igalia.com>
Cr-Commit-Position: refs/heads/master@{#559011}

content/browser/web_package/signed_exchange_consts.h

@@ -16,11 +16,14 @@ enum class SignedExchangeVersion { kB0, kB1 };
 // https://wicg.github.io/webpackage/draft-yasskin-httpbis-origin-signed-exchanges-impl.html#application-signed-exchange
 
 constexpr char kCertSha256Key[] = "certSha256";
+constexpr char kCertUrl[] = "certUrl";
 constexpr char kDateKey[] = "date";
 constexpr char kExpiresKey[] = "expires";
 constexpr char kHeadersKey[] = "headers";
+constexpr char kIntegrity[] = "integrity";
 constexpr char kMethodKey[] = ":method";
 constexpr char kSignature[] = "signature";
+constexpr char kSig[] = "sig";
 constexpr char kStatusKey[] = ":status";
 constexpr char kUrlKey[] = ":url";
 constexpr char kValidityUrlKey[] = "validityUrl";

content/browser/web_package/signed_exchange_header_parser.cc

@@ -215,21 +215,21 @@ SignedExchangeHeaderParser::ParseSignature(
     signatures.push_back(Signature());
     Signature& sig = signatures.back();
     sig.label = value.label;
-    sig.sig = value.params["sig"];
+    sig.sig = value.params[kSig];
     if (sig.sig.empty()) {
       signed_exchange_utils::ReportErrorAndEndTraceEvent(
           devtools_proxy, "SignedExchangeHeaderParser::ParseSignature",
           "'sig' parameter is not set,");
       return base::nullopt;
     }
-    sig.integrity = value.params["integrity"];
+    sig.integrity = value.params[kIntegrity];
     if (sig.integrity.empty()) {
       signed_exchange_utils::ReportErrorAndEndTraceEvent(
           devtools_proxy, "SignedExchangeHeaderParser::ParseSignature",
           "'integrity' parameter is not set.");
       return base::nullopt;
     }
-    sig.cert_url = GURL(value.params["certUrl"]);
+    sig.cert_url = GURL(value.params[kCertUrl]);
     if (!sig.cert_url.is_valid() || sig.cert_url.has_ref()) {
       // TODO(https://crbug.com/819467) : When we will support "ed25519Key", the
       // params may not have "certUrl".