Disk cache: move eviction code to a separate file....

net/disk_cache/rankings.cc

Index: net/disk_cache/rankings.cc
===================================================================
--- net/disk_cache/rankings.cc	(revision 7126)
+++ net/disk_cache/rankings.cc	(working copy)
@@ -495,6 +495,8 @@
     if (my_tail.value() == node->address().value())
       return NULL;
     Addr address(node->Data()->next);
+    if (address.value() == node->address().value())
+      return NULL;  // Another tail? fail it.
     next.reset(new CacheRankingsBlock(backend_->File(address), address));
   }
 
@@ -523,6 +525,8 @@
     if (my_head.value() == node->address().value())
       return NULL;
     Addr address(node->Data()->prev);
+    if (address.value() == node->address().value())
+      return NULL;  // Another head? fail it.
     prev.reset(new CacheRankingsBlock(backend_->File(address), address));
   }