Fix AmountOfFreeDiskSpace to be able to differentiate an error...

net/disk_cache/mem_backend_impl.cc

Index: net/disk_cache/mem_backend_impl.cc
===================================================================
--- net/disk_cache/mem_backend_impl.cc	(revision 2424)
+++ net/disk_cache/mem_backend_impl.cc	(working copy)
@@ -43,7 +43,7 @@
 
   int64 total_memory = base::SysInfo::AmountOfPhysicalMemory();
 
-  if (total_memory < 0) {
+  if (total_memory <= 0) {
     max_size_ = kDefaultCacheSize;
     return true;
   }