Plug leaked string stream debug object cache in Isolate.

BUG=
R=danno@chromium.org

Review URL: https://codereview.chromium.org/18324007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15411 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/isolate.cc

@@ -29,6 +29,7 @@
 
 #include "v8.h"
 
+#include "allocation-inl.h"
 #include "ast.h"
 #include "bootstrapper.h"
 #include "codegen.h"
@@ -2025,6 +2026,9 @@ Isolate::~Isolate() {
   delete global_handles_;
   global_handles_ = NULL;
 
+  delete string_stream_debug_object_cache_;
+  string_stream_debug_object_cache_ = NULL;
+
   delete external_reference_table_;
   external_reference_table_ = NULL;