Use same blob format for internal and external snapshots.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 5ba15f8d620ab67d0da0243774c98022ca6d19e8..0200dc013062933f6be7d402626b7d6e53c00eb8 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -357,7 +357,6 @@ source_set("v8_nosnapshot") {
     "$target_gen_dir/libraries.cc",
     "$target_gen_dir/experimental-libraries.cc",
     "src/snapshot-empty.cc",
-    "src/snapshot-common.cc",
   ]
 
   configs -= [ "//build/config/compiler:chromium_code" ]
@@ -379,7 +378,6 @@ source_set("v8_snapshot") {
     "$target_gen_dir/libraries.cc",
     "$target_gen_dir/experimental-libraries.cc",
     "$target_gen_dir/snapshot.cc",
-    "src/snapshot-common.cc",
   ]
 
   configs -= [ "//build/config/compiler:chromium_code" ]
@@ -894,6 +892,7 @@ source_set("v8_base") {
     "src/serialize.h",
     "src/small-pointer-list.h",
     "src/smart-pointers.h",
+    "src/snapshot-common.cc",
     "src/snapshot-source-sink.cc",
     "src/snapshot-source-sink.h",
     "src/snapshot.h",