Cache Backend Proxy to intercept all cache events from the IO thread.

net/disk_cache/cache_creator.cc

Index: net/disk_cache/cache_creator.cc
diff --git a/net/disk_cache/cache_creator.cc b/net/disk_cache/cache_creator.cc
index d8344a9a65b4dac976161aeb470d3bdd58329be2..b1a77dd22ef4485b1225bf64c798673fb56764d2 100644
--- a/net/disk_cache/cache_creator.cc
+++ b/net/disk_cache/cache_creator.cc
@@ -11,6 +11,10 @@
 #include "net/disk_cache/mem_backend_impl.h"
 #include "net/disk_cache/simple/simple_backend_impl.h"
 
+#ifdef USE_TRACING_CACHE_BACKEND
+#include "net/disk_cache/tracing_cache_backend.h"
+#endif
+
 namespace {
 
 // Builds an instance of the backend depending on platform, type, experiments
@@ -111,6 +115,9 @@ void CacheCreator::DoCallback(int result) {
       created_cache_ = *backend_;
     else
       *backend_ = created_cache_;
+#ifdef USE_TRACING_CACHE_BACKEND
+    *backend_ = new disk_cache::TracingCacheBackend(*backend_);
+#endif
   } else {
     LOG(ERROR) << "Unable to create cache";
     *backend_ = NULL;
@@ -160,5 +167,4 @@ int CreateCacheBackend(net::CacheType type, const base::FilePath& path,
   return creator->Run();
 }
 
-
 }  // namespace disk_cache