Introduce mkgrokdump to update tools/v8heapconst.py.

test/BUILD.gn

Index: test/BUILD.gn
diff --git a/test/BUILD.gn b/test/BUILD.gn
index 519c1d3a0e1e62a25bf34fe49b4664fc390e2db8..440f34054538a3500827feac2332938fadeb2989 100644
--- a/test/BUILD.gn
+++ b/test/BUILD.gn
@@ -11,6 +11,7 @@ group("gn_all") {
   deps = [
     ":default_tests",
     "inspector:inspector-test",
+    "mkgrokdump:mkgrokdump",
   ]
 
   if (host_os != "mac" || !is_android) {
@@ -48,6 +49,7 @@ group("default_tests") {
       ":intl_run",
       ":message_run",
       ":mjsunit_run",
+      ":mkgrokdump_run",
       ":preparser_run",
       ":unittests_run",
     ]
@@ -164,6 +166,14 @@ v8_isolate_run("mjsunit") {
   isolate = "mjsunit/mjsunit.isolate"
 }
 
+v8_isolate_run("mkgrokdump") {
+  deps = [
+    "mkgrokdump:mkgrokdump",
+  ]
+
+  isolate = "mkgrokdump/mkgrokdump.isolate"
+}
+
 v8_isolate_run("mozilla") {
   deps = [
     "..:d8_run",