Add an IO thread index bitmap to disk cache.

net/disk_cache/backend_impl.h

Index: net/disk_cache/backend_impl.h
diff --git a/net/disk_cache/backend_impl.h b/net/disk_cache/backend_impl.h
index 91faa83373b510c7ede43ec2914adfb755dd70ea..e97a7b047276ec0b31087dc4fa3795d29b8dd5ae 100644
--- a/net/disk_cache/backend_impl.h
+++ b/net/disk_cache/backend_impl.h
@@ -9,7 +9,10 @@
 
 #include "base/file_path.h"
 #include "base/hash_tables.h"
+#include "base/memory/ref_counted.h"
+#include "base/message_loop_proxy.h"
 #include "base/timer.h"
+#include "net/disk_cache/bitmap.h"
 #include "net/disk_cache/block_files.h"
 #include "net/disk_cache/disk_cache.h"
 #include "net/disk_cache/eviction.h"
@@ -60,7 +63,9 @@ class NET_EXPORT_PRIVATE BackendImpl : public Backend {
   // Performs general initialization for this current instance of the cache.
   int Init(const CompletionCallback& callback);
 
-  // Performs the actual initialization and final cleanup on destruction.
+  // Performs the actual initialization and final cleanup on destruction. If
+  // |async_thread| is non null, then |bitmap_| may be initialized on that

[rvargas (doing something else), 2013/02/12 01:58:33]

I'm guessing the comment is stale now.

+  // thread, otherwise |bitmap_| is left unchanged.
   int SyncInit();
   void CleanupCache();
 
@@ -233,6 +238,9 @@ class NET_EXPORT_PRIVATE BackendImpl : public Backend {
   // Sets an explicit set of BackendFlags.
   void SetFlags(uint32 flags);
 
+  // Clears the index bitmap for tests.
+  void ClearIndexBitmapForTest();
+
   // Clears the counter of references to test handling of corruptions.
   void ClearRefCountForTest();
 
@@ -384,6 +392,8 @@ class NET_EXPORT_PRIVATE BackendImpl : public Backend {
   bool first_timer_;  // True if the timer has not been called.
   bool user_load_;  // True if we see a high load coming from the caller.
 
+  Bitmap index_bitmap_;
+
   net::NetLog* net_log_;
 
   Stats stats_;  // Usage statistics.