RFC: use some in-memory state in SimpleCache to quickly cache-miss some CantConditionalize cases

net/http/http_cache.h

Index: net/http/http_cache.h
diff --git a/net/http/http_cache.h b/net/http/http_cache.h
index 91214c179f9fb27051873c40a331821b3198386e..3022fed81175828a87c20e5767c29d7acc23fae3 100644
--- a/net/http/http_cache.h
+++ b/net/http/http_cache.h
@@ -31,6 +31,7 @@
 #include "net/base/load_states.h"
 #include "net/base/net_export.h"
 #include "net/base/request_priority.h"
+#include "net/disk_cache/disk_cache.h"
 #include "net/http/http_network_session.h"
 #include "net/http/http_transaction_factory.h"
 
@@ -44,7 +45,6 @@ class ProcessMemoryDump;
 }  // namespace base
 
 namespace disk_cache {
-class Backend;
 class Entry;
 }  // namespace disk_cache
 
@@ -68,6 +68,13 @@ class NET_EXPORT HttpCache : public HttpTransactionFactory {
     DISABLE
   };
 
+  // ### probably don't need to blow all of 3 bits on this.
+  enum OracleByteHints {
+    OBH_ZERO_LIFETIME = 1,
+    OBH_RESPONSE_CANT_CONDITIONALIZE = 2,
+    OBH_UNUSED_SINCE_PREFETCH = 4
+  };
+
   // A BackendFactory creates a backend object to be used by the HttpCache.
   class NET_EXPORT BackendFactory {
    public:
@@ -370,8 +377,12 @@ class NET_EXPORT HttpCache : public HttpTransactionFactory {
 
   // Opens the disk cache entry associated with |key|, returning an ActiveEntry
   // in |*entry|. |trans| will be notified via its IO callback if this method
-  // returns ERR_IO_PENDING.
-  int OpenEntry(const std::string& key, ActiveEntry** entry,
+  // returns ERR_IO_PENDING. If creating a new entry, will pass it through
+  // |trans->MaybeRejectBasedOnMemoryEntryData|, returning
+  // ERR_CACHE_ENTRY_NOT_SUITABLE after dooming the key if that rejects the
+  // entry.
+  int OpenEntry(const std::string& key,
+                ActiveEntry** entry,
                 Transaction* trans);
 
   // Creates the disk cache entry associated with |key|, returning an