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

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

Index: ppapi/native_client/src/trusted/plugin/pnacl_options.cc
diff --git a/ppapi/native_client/src/trusted/plugin/pnacl_options.cc b/ppapi/native_client/src/trusted/plugin/pnacl_options.cc
index ad31e88cce18da5e95acdbd7da6fcd7c6a9cf23d..e1c6b4befd63b3fa5f72b74fbb59aead74916099 100644
--- a/ppapi/native_client/src/trusted/plugin/pnacl_options.cc
+++ b/ppapi/native_client/src/trusted/plugin/pnacl_options.cc
@@ -9,6 +9,21 @@
 
 #include "native_client/src/include/nacl_string.h"
 
+namespace {
+
+nacl::string ReplaceBadFSChars(nacl::string str,
+                               const nacl::string& bad_chars,
+                               const nacl::string& replacement) {
+  size_t replace_pos = str.find_first_of(bad_chars);
+  while (replace_pos != nacl::string::npos) {
+    str = str.replace(replace_pos, 1, replacement);
+    replace_pos = str.find_first_of(bad_chars);
+  }
+  return str;
+}
+
+}  // namespace
+
 namespace plugin {
 
 // Default to -O0 for now.
@@ -17,15 +32,24 @@ PnaclOptions::PnaclOptions() : translate_(false), opt_level_(0) { }
 PnaclOptions::~PnaclOptions() {
 }
 
-nacl::string PnaclOptions::GetCacheKey() {
+nacl::string PnaclOptions::GetCacheKey() const {
   // TODO(jvoung): We need to read the PNaCl translator's manifest
   // to grab the NaCl / PNaCl ABI version too.
   nacl::stringstream ss;
   // Cast opt_level_ as int so that it doesn't think it's a char.
   ss << "-O:" << static_cast<int>(opt_level_)
      << ";flags:" << experimental_flags_
-     <<  ";bitcode_hash:" << bitcode_hash_;
-  return ss.str();
+     <<  ";cache_validators:" << cache_validators_;
+  // HTML5 FileSystem-based cache does not allow some characters which
+  // may appear in URLs, ETags, or Last-Modified times.  Once we move to
+  // our own cache-backend, it will be more tolerant of various cache
+  // key values.
+  // See: http://dev.w3.org/2009/dap/file-system/file-dir-sys.html#naming-restrictions
+  nacl::string key = ss.str();
+  key = ReplaceBadFSChars(key, "/", "_FWDSLASH_");
+  key = ReplaceBadFSChars(key, "\\", "_BCKSLASH_");
+  key = ReplaceBadFSChars(key, "\0", "_NULL_");
+  return key;
 }
 
 void PnaclOptions::set_opt_level(int8_t l) {
@@ -40,7 +64,7 @@ void PnaclOptions::set_opt_level(int8_t l) {
   opt_level_ = l;
 }
 
-std::vector<char> PnaclOptions::GetOptCommandline() {
+std::vector<char> PnaclOptions::GetOptCommandline() const {
   std::vector<char> result;
   std::vector<nacl::string> tokens;