Generate grokdump constants with 'make grokdump' now.

src/d8.h

Index: src/d8.h
diff --git a/src/d8.h b/src/d8.h
index 4f04342cf4dffb267776901f512f46d4fde1e5a4..3b06985ca25d45e950e35f3bcbc9a9b92425b3fe 100644
--- a/src/d8.h
+++ b/src/d8.h
@@ -231,6 +231,7 @@ class ShellOptions {
      stress_deopt(false),
      interactive_shell(false),
      test_shell(false),
+     dump_heap_constants(false),
      num_isolates(1),
      isolate_sources(NULL) { }
 
@@ -254,6 +255,7 @@ class ShellOptions {
   bool stress_deopt;
   bool interactive_shell;
   bool test_shell;
+  bool dump_heap_constants;
   int num_isolates;
   SourceGroup* isolate_sources;
 };