Add SimpleCache index file heuristics

net/disk_cache/simple/simple_index.cc

Index: net/disk_cache/simple/simple_index.cc
diff --git a/net/disk_cache/simple/simple_index.cc b/net/disk_cache/simple/simple_index.cc
index c2b73b9c80716577363e59f05a4387de37bc4181..e4a7a225f25d764d2a51389aa8631b1f7382199b 100644
--- a/net/disk_cache/simple/simple_index.cc
+++ b/net/disk_cache/simple/simple_index.cc
@@ -9,6 +9,7 @@
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/file_util.h"
+#include "base/file_util.h"
 #include "base/logging.h"
 #include "base/message_loop.h"
 #include "base/pickle.h"
@@ -173,6 +174,8 @@ void SimpleIndex::InsertInEntrySet(
 }
 
 void SimpleIndex::PostponeWritingToDisk() {
+  if (!initialized_)
+    return;
   const base::TimeDelta file_age = base::Time::Now() - last_write_to_disk_;
   if (file_age > base::TimeDelta::FromSeconds(kMaxWriteToDiskDelaySecs) &&
       write_to_disk_timer_.IsRunning()) {
@@ -194,21 +197,24 @@ void SimpleIndex::LoadFromDisk(
     const base::FilePath& index_filename,
     base::SingleThreadTaskRunner* io_thread,
     const IndexCompletionCallback& completion_callback) {
-  scoped_ptr<EntrySet> index_file_entries =
-      SimpleIndexFile::LoadFromDisk(index_filename);
+  bool restore_from_disk = SimpleIndexFile::IndexFileIsStale(index_filename);
+
+  scoped_ptr<EntrySet> index_file_entries;
+  if (!restore_from_disk) {
+    index_file_entries = SimpleIndexFile::LoadFromDisk(index_filename);
+  }
 
-  bool force_index_flush = false;
   if (!index_file_entries.get()) {
     index_file_entries = SimpleIndex::RestoreFromDisk(index_filename);
     // When we restore from disk we write the merged index file to disk right
     // away, this might save us from having to restore again next time.
-    force_index_flush = true;
+    restore_from_disk = true;
   }
 
   io_thread->PostTask(FROM_HERE,
                       base::Bind(completion_callback,
                                  base::Passed(&index_file_entries),
-                                 force_index_flush));
+                                 restore_from_disk));
 }
 
 // static