Use HTTP response headers for PNaCl caching instead of bitcode hash.

ppapi/native_client/src/trusted/plugin/json_manifest.cc

Index: ppapi/native_client/src/trusted/plugin/json_manifest.cc
diff --git a/ppapi/native_client/src/trusted/plugin/json_manifest.cc b/ppapi/native_client/src/trusted/plugin/json_manifest.cc
index d1f70ff39f96e278f197b6151e01f34c58b7818b..412d84d56658aaec85561eaeb09d1062f880b586 100644
--- a/ppapi/native_client/src/trusted/plugin/json_manifest.cc
+++ b/ppapi/native_client/src/trusted/plugin/json_manifest.cc
@@ -41,7 +41,6 @@ const char* const kPnaclTranslateKey = "pnacl-translate";
 const char* const kUrlKey =            "url";
 
 // Pnacl keys
-const char* const kCacheIdentityKey = "sha256";
 const char* const kOptLevelKey = "-O";
 const char* const kPnaclExperimentalFlags = "experimental_flags";
 
@@ -54,7 +53,6 @@ const char* const kPnaclExperimentalFlags = "experimental_flags";
 //     "portable": {
 //       "pnacl-translate": {
 //         "url": "myprogram.pexe",
-//         "sha256": "...",
 //         "-O": 0
 //       }
 //     }
@@ -153,7 +151,6 @@ bool IsValidUrlSpec(const Json::Value& url_spec,
   };
   static const char* kManifestUrlSpecPlusOptional[] = {
     kUrlKey,
-    kCacheIdentityKey
   };
   if (!IsValidDictionary(url_spec, container_key, parent_key,
                          kManifestUrlSpecPlusOptional,
@@ -274,9 +271,6 @@ void GrabUrlAndPnaclOptions(const Json::Value& url_spec,
                             nacl::string* url,
                             PnaclOptions* pnacl_options) {
   *url = url_spec[kUrlKey].asString();
-  if (url_spec.isMember(kCacheIdentityKey)) {
-    pnacl_options->set_bitcode_hash(url_spec[kCacheIdentityKey].asString());
-  }
   if (url_spec.isMember(kOptLevelKey)) {
     uint32_t opt_raw = url_spec[kOptLevelKey].asUInt();
     // Clamp the opt value to fit into an int8_t.