Fix warnings on Win64.

src/scopes.cc

Index: src/scopes.cc
diff --git a/src/scopes.cc b/src/scopes.cc
index 81fb9ead18fce9311962a16503f905addf336533..7da06cdbc03389544ac4f80b86dde5b0c878d9d9 100644
--- a/src/scopes.cc
+++ b/src/scopes.cc
@@ -42,7 +42,7 @@ class ZoneAllocator: public Allocator {
   /* nothing to do */
   virtual ~ZoneAllocator()  {}
 
-  virtual void* New(size_t size)  { return Zone::New(size); }
+  virtual void* New(size_t size)  { return Zone::New(static_cast<int>(size)); }
 
   /* ignored - Zone is freed in one fell swoop */
   virtual void Delete(void* p)  {}