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

net/disk_cache/simple/simple_version_upgrade.cc

Index: net/disk_cache/simple/simple_version_upgrade.cc
diff --git a/net/disk_cache/simple/simple_version_upgrade.cc b/net/disk_cache/simple/simple_version_upgrade.cc
index 1c4a7ba2b2bd569b593d5da059b96c0a0bce0586..b21dbbd22e7fb030649d706e57e23722c51afbff 100644
--- a/net/disk_cache/simple/simple_version_upgrade.cc
+++ b/net/disk_cache/simple/simple_version_upgrade.cc
@@ -198,6 +198,12 @@ bool UpgradeSimpleCacheOnDisk(const base::FilePath& path,
     // the V7 index reader is backwards compatible.
     version_from++;
   }
+
+  if (version_from == 7) {
+    // Likewise, V7 -> V8 is handled entirely by the index reader.
+    version_from++;
+  }
+
   DCHECK_EQ(kSimpleVersion, version_from);
 
   if (!new_fake_index_needed)