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

net/disk_cache/simple/simple_index.h

Index: net/disk_cache/simple/simple_index.h
diff --git a/net/disk_cache/simple/simple_index.h b/net/disk_cache/simple/simple_index.h
index 6740c2c91e2b810caa5d2092d93baff6b616c85e..36f13989049b618aa24b29c5b5adcb4630a87a0b 100644
--- a/net/disk_cache/simple/simple_index.h
+++ b/net/disk_cache/simple/simple_index.h
@@ -57,10 +57,12 @@ class NET_EXPORT_PRIVATE EntryMetadata {
 
   uint32_t GetEntrySize() const;
   void SetEntrySize(base::StrictNumeric<uint32_t> entry_size);
+  uint8_t GetOracleByte() const;
+  void SetOracleByte(uint8_t oracle_byte);
 
   // Serialize the data into the provided pickle.
   void Serialize(base::Pickle* pickle) const;
-  bool Deserialize(base::PickleIterator* it);
+  bool Deserialize(base::PickleIterator* it, bool has_oracle_byte);
 
   static base::TimeDelta GetLowerEpsilonForTimeComparisons() {
     return base::TimeDelta::FromSeconds(1);
@@ -79,7 +81,8 @@ class NET_EXPORT_PRIVATE EntryMetadata {
   // are originally calculated as >32-bit types, the actual necessary size for
   // each shouldn't exceed 32 bits, so we use 32-bit types here.
   uint32_t last_used_time_seconds_since_epoch_;
-  uint32_t entry_size_;  // Storage size in bytes.
+  // Storage size in bytes... with oracle byte packed into lower 8 bites.
+  uint32_t entry_size_;
 };
 static_assert(sizeof(EntryMetadata) == 8, "incorrect metadata size");
 
@@ -123,6 +126,10 @@ class NET_EXPORT_PRIVATE SimpleIndex
   // Check whether the index has the entry given the hash of its key.
   bool Has(uint64_t entry_hash) const;
 
+  // Like above, but also writes out the oracle byte (or 0) into |*oracle_byte|
+  // if returned true.
+  bool HasWithOracleByte(uint64_t entry_hash, uint8_t* oracle_byte);
+
   // Update the last used time of the entry with the given key and return true
   // iff the entry exist in the index.
   bool UseIfExists(uint64_t entry_hash);
@@ -134,6 +141,7 @@ class NET_EXPORT_PRIVATE SimpleIndex
   // entry.
   bool UpdateEntrySize(uint64_t entry_hash,
                        base::StrictNumeric<uint32_t> entry_size);
+  void UpdateEntryOracleByte(uint64_t entry_hash, uint8_t oracle_byte);
 
   using EntrySet = std::unordered_map<uint64_t, EntryMetadata>;