Fix win64 compilation (using static_cast)

Review URL: http://codereview.chromium.org/3225011

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5383 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/frames.cc

@@ -316,7 +316,7 @@ void StackFrame::IteratePc(ObjectVisitor* v,
                            Code* holder) {
   Address pc = *pc_address;
   ASSERT(holder->contains(pc));
-  unsigned pc_offset = pc - holder->instruction_start();
+  unsigned pc_offset = static_cast<unsigned>(pc - holder->instruction_start());
   Object* code = holder;
   v->VisitPointer(&code);
   if (code != holder) {