Introduce mkgrokdump to update tools/v8heapconst.py.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 1ab72e343d99249acf10d7a67a1866842c2d44ce..9d08cf29338f194dd11c1939d00195edecbb68b5 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -2613,6 +2613,28 @@ if (current_toolchain == v8_snapshot_toolchain) {
   }
 }
 
+v8_executable("mkgrokdump") {
+  # mkgrokdump is used to create tools/v8heapconst.py.
+  visibility = [ ":*" ]  # Only targets in this file can depend on this.
+
+  sources = [
+    "tools/mkgrokdump.cc",
+  ]
+
+  configs = [
+    ":external_config",
+    ":internal_config",
+  ]
+
+  deps = [
+    ":v8",
+    ":v8_libbase",
+    ":v8_libplatform",
+    "//build/config/sanitizers:deps",
+    "//build/win:default_exe_manifest",
+  ]
+}
+
 ###############################################################################
 # Public targets
 #
@@ -2628,6 +2650,7 @@ group("gn_all") {
 
   deps = [
     ":d8",
+    ":mkgrokdump",
     ":v8_fuzzers",
     ":v8_hello_world",
     ":v8_parser_shell",