Make the blockfile cache an optional build product for chrome target.

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 9c8538b7efc67ebbf82c52c26cd01b18c28c4983..e4f9bedac12be61d39cf6d0d322680c1f3b03f48 100644
--- a/net/disk_cache/cache_creator.cc
+++ b/net/disk_cache/cache_creator.cc
@@ -13,6 +13,10 @@
 #include "net/disk_cache/simple/simple_backend_impl.h"
 #include "net/disk_cache/v2/backend_impl.h"
 
+#ifdef USE_BLOCKFILE_CACHE_BACKEND
+#include "net/disk_cache/blockfile/backend_impl.h"
+#endif
+
 #ifdef USE_TRACING_CACHE_BACKEND
 #include "net/disk_cache/tracing_cache_backend.h"
 #endif
@@ -91,6 +95,8 @@ int CacheCreator::Run() {
     return simple_cache->Init(
         base::Bind(&CacheCreator::OnIOComplete, base::Unretained(this)));
   }
+
+#if defined(USE_BLOCKFILE_CACHE_BACKEND)
   disk_cache::BackendImpl* new_cache =
       new disk_cache::BackendImpl(path_, thread_.get(), net_log_);
   created_cache_.reset(new_cache);
@@ -101,6 +107,9 @@ int CacheCreator::Run() {
       base::Bind(&CacheCreator::OnIOComplete, base::Unretained(this)));
   DCHECK_EQ(net::ERR_IO_PENDING, rv);
   return rv;
+#else
+  return net::ERR_FAILED;
+#endif
 }
 
 void CacheCreator::DoCallback(int result) {
@@ -157,7 +166,7 @@ int CreateCacheBackend(net::CacheType type,
   }
   DCHECK(thread);
   CacheCreator* creator = new CacheCreator(path, force, max_bytes, type,
-                                           backend_type, kNone,
+                                           backend_type, 0,
                                            thread, net_log, backend, callback);
   return creator->Run();
 }